252 SIDNKY V. HARMER. 



lated where it begins to descend, and the angle is usually 

 greatly thickened by a tubercular transverse portion, which 

 may extend, in the middle, proximally so as to obliterate 

 some of the pores. The parts of the cryptocyst which bound 

 the lateral recesses are vertical. The tube is complete all 

 round, its wall being unusually well developed on its deep or 

 basal side. The opening is well raised above the basal wall 

 of the zooecium. The cavity of the median process is not 

 very deep, the convex roof of the tube forming its floor, and 

 being clearly exposed to view from above. The lateral and 

 distal boundaries of the cavity are well developed. A view 

 of the basal wall of the zooecia shows clearly the insertion 

 of the cryptocyst. The epithecal sclerites are short and deli- 

 cate, just overlapping- the angulated edge of the cryptocyst, 

 but not nearly reaching the operculum, b zooecia have not 

 been observed. 



The B opercula (fig. 23) are very rare, and only three (one 

 of them damaged) have been found. They are short and 

 broad, and they agree in possessing a very strong fl-shaped 

 main sclerite, the insertion of the occlusor muscle being of 

 great size, and much elongated transversely. The proximal 

 projections of the main sclerite are much prolonged into 

 spout-like lobes, which are concave externally. The basal 

 sclerite is strong. This operculum is almost unique among 

 B opercula in having no submarginal ^ teeth, these structures 

 being, however, represented by vestiges, which are merely 

 inconspicuous rounded lobules. The a opercula (fig. 22) are 

 small, and belong to the undifferentiated type ; the buttresses 

 of the proximal projections of the main sclerite are well 

 developed. The average diameter of b is 530 ju, that of the 

 specimen figured being 560 fx. The average diameter of a is 

 420 f.1, the range being from 370 to 470 fx. 



' Tlie teeth do not always appear submarginal in the sketches. The 

 boiling with strong nitric acid is ])robably responsible for the disappearance 

 of the very delicate margin which I find in the opercula of many species (as 

 in fig. 38) outside the tooth-bearing sclerite. 1 believe this delicate margin 

 to be a normal feature of the opercula. 



