Sea water originally at pH8·2 became as alkaline as pH9·4 by the photosynthetic action of Ulva in removing carbonic acid. This degree of alkalinity did not prove injurious to Ulva, but exposure to it for two and a half hours at 27° C. sufficed to increase the permeability of the superficial cells of Ceramium rubrum irreversibly and fatally. Similar though less rapid changes brought about the death of numerous Vorticellæ epiphytic on Ceramium. The criteria for living cells were permeability to neutral red and impermeability to brom cresol purple. Dead cells do not retain neutral red specifically and are permeable to brom cresol purple.

It is suggested that the above facts have a bearing upon the distribution of these and similar algæ upon the shore.

Formalin, which is permanently non-acid and only slightly alkaline, close to pH9, may be prepared by the addition of borax till a good red colour is shown with phenolphthalein, or a slaty blue with thymol blue, when added to the diluted formalin.

Distillation of formalin from solid magnesium carbonate gives an acid product, which is at pH4·4.

Formalin neutralised with sodium hydroxide becomes acid on standing, the change being more rapid in sunlight than in the dark. A reaction of pH5·2 was reached in fifty-six days in light, the initial value being pH8·0. Commercial formalin, “ 40 per cent,” may be as acid as pH2·8.

Much discussion has recently taken place over the peridinian described by Bergh (1882) as Diplopsalis lenticula, and certainly three distinct species have severally been designated as the original. As it is a name frequently to be found in the International Plankton lists, it is important that we should be clear as to which species we are noting, and as recent research at Plymouth has shown that all the three are common in the district it seems worth while to investigate them once more. The question is interesting also from the point of view of phylogeny, as in these species we have close relatives of Peridinium proper which seem to indicate the method of evolution of that genus from simpler forms with fewer plates, and from this point of view alone they are well worth study.

In centrifuging samples of sea water from Plymouth Sound and some of the stations outside, some interesting forms of Exuviella were found. These are all minute, the largest measuring 22 µ in length, and consequently are easily overlooked, although one at least is abundant during the summer months. This species, which is the commonest Exuviella in the Plymouth district, has been identified as Exuviella perforata Gran, described by him from the North Sea (1915), and is a new record for the English Channel. As it appears to be very little known and its structure is unusual in several particulars, the following notes are not without interest.

In 1915 Gran (page 99, Fig. 7) describes and figures Exuviella perforata, a new species from the North Sea at a depth of 0–20 metres, occurring in the eastern part with a density of 100–760 specimens per litre. It is roundish oval or nearly circular in shape, measuring 22.5–25 µ long and 21–22.5 µ wide, with a broad girdle and thick shell (thickness of cell 14–17 µ). The character, however, that gives it peculiar distinction is the depression in the centre of each valve, as Gran puts it, “with a sharply confined point-shaped perforated deepening in the centre.” This separates it from any previously known species of Exuviella. The cell contents owing to contraction could not be described in detail, but in a footnote it is stated that living specimens from Arendal in March, 1914, had brown chromatophores. Cleve-Euler (1917) records an Exuviella, which he says may be E. perforata Gran, as occurring frequently in the Skaggerak, from 0 to 100 metres.

In centrifuged water and in very fine tow-nets there sometimes occurred an extremely small species of Phalacroma, which appears to be new.

The genus Ilyanthus was erected by Forbes (1840) for I. scoticus; little is known about that species, and its anatomy is undescribed. There is no evidence that any subsequently described species is really a genuine Ilyanthus, and the genus-name can only be used provisionally for others until I. scoticus can be dissected. Meanwhile the genus-name must be reserved for I. mitchellii, the main subject of this paper. Gosse described this species from a specimen which he saw in 1853 (see Actinologia, p. 232); it must have been in poor condition or semi-contracted, and his figure (PL. 8, Fig. 6) is quite misleading. Andres erected (1883, p. 462) a genus Mesacmœa for his Ilyanthus stellatus of 1880, and, as I hope to show below, M. stellata is either specifically or at any rate generically identical with I. mitchellii; so that Mesacmœa now becomes a synonym; if it should prove, later on, when I. scoticus can be examined, that I. mitchellii does not really agree with it, i.e. is no Ilyanthus, then the name Mesacmœa can be revived for mitchellii and stellatus. Carlgren (Actiniaria of the Danish Ingolf—Expedition, 1921) has given a few anatomical details of Me acmœa, gained from notes by Andres in his possession; they agree with my description of I. mitchellii as far as they go, but there are not enough of them to make a full understanding of the genus possible. In Andres' 1883 monograph will be found a description of another species, I. partenopeus (p. 459).

Parorchis acanthus is a Trematode described by Nicoll (1907) from the bursa Fabricii and rectum of the Herring Gull, Larus argentatus; in 1906 he first described it as Zeugorchis acanthus. Originally found at St. Andrews, it is now known to be common at Millport and also occurs in gulls from the Northumberland coast, and probably is abundant elsewhere. Nicoll found it once in the Common Gull, Larus canus. In 1907 (Lebour, 1907) one of the present writers described a cercaria occurring in rediæ from Purpura lapillus. This was named Cercaria purpurœ sp. inq., and afterwards identified with young stages of Parorchis acanthus in the Herring Gull (Lebour, 1914). It was thus shown that the first host of this Trematode is Purpura lapillus and the final host the Herring Gull, but the intermediate host was unknown. Localities for the cercaria were Loch Ryan, Wigtownshire; Budle Bay, Fenham Flats and Cullercoats in Northumberland; Robin Hood's Bay in Yorkshire; and Millport. Adults occur at St. Andrews, Northumberland coast and Millport, as already stated.

The Cercaria appeared to be closely related to Echinostomum cercariæ, and it was suggested (Lebour, 1914) that the intermediate host would probably be some marine bivalve, as it is often so with Echinostomum (e.g. E. secundum in Mytilus edulis and Cardium edule, E. leptosomum in Scrobicularia tenuis). This suggestion now proves to be correct, and we are able to show that the intermediate host of Parorchis acanthus is Mytilus edulis or Cardium edule.

On August 13th, 1921, at the Millport Station some larval cercariæ were noticed by Elmhirst swimming in a small glass aquarium, which contained a collection of Purpura lapillus, Cardium edule and Mytilus edulis.

When collecting on the shores in the Plymouth area, while a member of the Easter Class at the Marine Biological Laboratory, Plymouth, in 1921, I was struck by the absence above low-water mark of Echinus esculentus, as contrasted with its abundance in this zone at Port Erin in the Isle of Man; for there, as Chadwick states, “it may be collected by hand on the beach, and on the ruined breakwater at low-water of spring tides.” There is no record of this species except below tide-marks in the “Plymouth Marine Invertebrate Fauna” list (Journ. Marine Biological Association, Vol. VII, 1904).

In 1849 W. P. Cocks, in the Trans. Penzance Natural History and Antiquarian Society (“List of Echinodermata procured in Falmouth and Neighbourhood from 1843 to 1849”), recorded the occurrence of this species thus:—

“Echinus sphœra.—Trawl refuse; common: young specimen found attached to stones, low-water mark.”

Later (1887–8), in the same journal, G. F. Tregelles, in a paper on “Echinodermata of Mount's Bay,” makes the following statement of the species of the genus Echinus: “The commonest and largest is E. esculentus (Pennant) [E. sphœra Forbes], which literally swarms off this coast at all depths. It is brought in by trawlers; it is found in crab-pots, into which it climbs laboriously after bait; the seaweed gatherers obtain them in from one to two fathoms of water. The Mouse-hole fishermen call them ‘zarts,’ doubtless an old Cornish word.”

Four ordinary meetings of the Council were held during the year, at which the average attendance was fourteen. A formal inspection of the Laboratory was carried out on behalf of the Council by Dr. G. P. Bidder, the other members of the Committee appointed for the purpose being prevented from travelling to Plymouth by a threatened railway strike. The thanks of the Association are due to the Council of the Royal Society, in whose rooms the meetings have been held.

Allen, E. J. Regeneration and Reproduction of the Syllid Procerastea. Phil. Trans. Roy. Soc., B. Vol. CCXI, pp. 131–177.