The controversy which has arisen in recent years in New Zealand regarding the problem of the Pleistocene glaciation of that country resolves itself into the two following main questions:—

1. Was there any glaciation in the North Island?

2. Was there an ice-sheet covering the South Island?

Starting with the bed labelled “Bieavea bed” by Rowe, the following generalized section represents the downward sequence in the Isle of Wight.

The characters of the apical system of a series of Holectypus hemisphæricus from the same horizon at two localities in Dorsetshire are analysed and described. It is found that the average relations of the plates of the system are different at the two localities, although certain numbers of identical forms occur at both. Out of 189 specimens (from both localities), 40 show serious departures from the normal type. These abnormalities are of three classes. One, the most prevalent, consists in the presence of madreporic pores on genital 3, in addition to the normal perforation of genital 2. This is regarded as a “progressive variant” in the direction of Discoides. The second, occurring in three specimens, consists in the interpolation of a supernumerary plate within the system. It is suggested that this may be either a “regressive variant” towards Acrosalenia, or a “progressive variant” towards Nucleolites (as illustrated by N.orlicularis). In neither case would this variation coincide with actual phyletic sequence, so that it is styled “parallel variation”. The third type of variant, seen in one specimen only, combines both the first and second types, and in addition shows an absence of genital 5 and a corresponding increase in the size of the posterior oculars, which meet round the back of the system. The variation in this specimen is interpreted as being “progressive” towards Discoides, “parallel progressive” or “regressive” towards Nucleolites or Acrosalenia respectively, and “progressive” towards Conulus. There are indications of a different series of variants in the Holectypus depressus from the Cornbrash. The high percentage of variation in the composition of the apical system of Holectypus is regarded as an indication of the evolutional activity of the genus, and of its near approximation in time and phylogeny to the common origin of many of the groups of Irregular Echinoids.

Diagnosis.—Asty incrusting, uniserial, with bilateral and unilateral branching; œcia dimorphic; normal œcia with short caudæ or without caudæ pyriform; termen a complete, high, narrow, oval ridge with few small spines on its circumference and, at the proximal-lateral corners of the aperture, a pair of stout spines which sometimes, if not always, bend towards one another and fuse in the middle line; apparently there are no spines around the distal end of the aperture; extra-terminal front-wall well-developed proximally, and arched; intra-terminal front-wall a wide, depressed lamina; aperture oval, sub-quadrate, somewhat constricted laterally; avicularia small, one, or a pair, placed laterally and somewhat distally with regard to each aperture, rather abruptly pointed with the distal ends curved towards the aperture they encompass; ovicells hyperstomial.