440 Mr. G. C. Crick on some 



umbilicus to near the edge of the periphery, where they are 

 bent abruptly backward and form on the periphery a deep 

 and wide hyponomic sinus; on the periphery the ornaments 

 are stronger and more regularly arranged, the ribs being 

 narrow and the interspaces a little wider than the ribs ; at the 

 anterior end of the body-chamber the riblets almost dis- 

 appear both on the sides and on the periphery ; the whole 

 surface also with very fine raised lines, having the same 

 direction as the riblets and crossing the inner area in a feeble 

 anteriorly convex curve. " Wrinkle-layer " with minute 

 blunt tubercles, which have a tendency to arrange themselves 

 in transverse stria} near the umbilical portion of the whorl, 

 while near the periphery they tend to dispose themselves in 

 longitudinal stria?. 



Dimensions. 



(i.) («.) (iii.) (iv.) 



Diameter of shell 97 mm. (100) 80 mm. (100) 62"5 mm. (100) 35 mm. (100) 



Width of umbilicus 



(at suture of shell). 30 „ (309) 23 „ (287) 17 „ (27-1) 13 „ (37'1) 

 Width of umbilicus 



(at its margin) 35 „ (36-2) 28 „ (350) 21 „ (33 6) 14 „ (400) 



Height of outer whorl 41 „ (422) 32-5 „ (40'6) 265 „ (42 4) 14 „ (40-0) 

 Ditto above preceding 



whorl 26*,, (268) 24 „ (300) 18* „ (28-8) 105 „ (30-0) 



Thickness of outer 



whorl 44*,, (45-3) 39 5 „ (493) 31-5 „ (50 4) 19 „ (54-?) 



Remarks. The present species is represented by four 

 examples, the dimensions of which are given above. Three 

 of these (ii., iii., and iv.) are in Dr. Foord's collection, the 

 other (i.) is in thecollection of the British Museum (no.G. 29S). 

 Compared with the adult, young examples have relatively 

 wider whorls and a wider umbilicus in proportion to the 

 diameter of the shell • they have also coarser ornaments. Up 

 to a diameter of about 22 millim. the riblets pass over the 

 margin of the umbilicus on to the umbilical zone of the whorl. 



One of Dr. Foord's specimens (example ii. referred to 

 above) shows the " wrinkle-layer " very clearly. 



The example in the British Museum is labelled " Gonia- 

 tites Brownii" apparently in Mr. Baily's handwriting, but 

 the specimen agrees neither with M'Coy's figure nor with his 

 description of that species \. 



For this species the name Pericyclus Bailyi is proposed, 

 after Mr. W. H. Baily, the late Palaeontologist of the Geolo- 

 gical Survey of Ireland. 



* Approximately. t See supra, p. 438, footnote. 



