436 Mr. G. C. Crick on some 



Remarks. The example in Dr. Foord's collection that is 

 selected as the type specimen is figured in the accompanying 

 figure (fig. 3) and its dimensions are given above (i.). This 

 appears to be the usual form of the species and is the chief 

 basis of the above diagnosis. But besides this there is a 

 form so closely related that it is considered to be specifically 

 identical, in which the whorls are somewhat more inflated 

 (being a little wider than high) and the umbilicus relatively 

 wider than in the type specimen. The dimensions of such an 

 example are also given above (iv.). 



There are five examples of this species in Dr. Foord's 

 collection, all from St. Doulagh's, Co. Dublin, Ireland. There 

 are also two fragments (the locality of which is not recorded) 

 in the British Museum collection (nos. C. 255 a & b) that are 

 referred to this species with some doubt, especially the example 

 C. 255 b. The specimen C. 255 a may have come from 

 St. Doulagh's, but the matrix of the example C. 255 5 differs 

 somewhat from the usual matrix of the St. Doulagh's 

 specimens. 



Affinities and Differences. This species is easily distin- 

 guished from Per. trapezoidal is * by its feebler ornaments 

 and very pronounced constrictions, and from Per. Foordif 

 by its less inflated whorls and the presence of constrictions. 



Horizon and Locality. Carboniferous Limestone : St. Dou- 

 lagh's, Co. Dublin, Ireland. 



Pericyclus clanensis, sp. n. (Figs. 4, 5.) 



Sp. char. Shell diseoidal, somewhat compressed, rather 

 involute ; greatest thickness at a short distance from the 

 edge of the umbilicus, rather more than four elevenths of the 

 diameter of the shell ; height of outer whorl about three 

 sevenths of the diameter of the shell. Whorls few (? num- 

 ber) ; inclusion nearly two thirds ; umbilicus shallow, rather 

 more than one fourth of the diameter of the shell in width, 

 with rounded margin. "Whorl semielliptical in cross-section, 

 somewhat higher than wide ; indented to rather more than 

 one third of its height by the preceding whorl ; periphery 

 broadly convex, imperfectly defined ; sides feebly convex, 

 somewhat flattened near the umbilicus; umbilical zone 

 narrow, convex, nearly perpendicular to the plane of sym- 

 metry of the shell, but sloping a little towards the umbilicus. 

 Body-chamber occupying rather more than the last whorl; 

 aperture not seen, but peristome (judging by the lines of 



* See supra, p. 432. t See supra, p. 430. 



