The graptolite here described was discovered first in the St. Tudwal's peninsula by Mr. T. C. Nicholas in 1912 in the Llanengan Mudstones, but it was not then regarded as distinct from Azygog. lapworthi, though it seemed to possess certain features not recognizable in the Lake District specimens, the only area from which that species had been previously recorded. The discoveryof numerous other specimens by Dr. Matley in the Lleyn peninsula and by Dr. Greenly in the Bangor area has served to show that the characters wherein this species differed from Azygog. lapworthi are permanent and of specific value, and since, moreover, it occurs at a distinctly higher horizon than Azygog. lapworthi, being characteristic of about the middle of the zone of Didymog. extensus, a description of it seems advisable. In general it has been noted that it is in many respects intermediate in character between Azygog. lapworthi on the one hand and Azygog. suecicus on the other, and it is perhaps significant that it occurs upon an horizon between the two.