TKRICYCLUS BAILYI. 



PEKirvcMS B.\ii,Yi, a. C. Crid: Plate XL, figs. 1—3. 



IS'J'J. Peeicyclus Bailyi. G. C. Crick. Ann. M;ii?. Nat. Hist,, ser. 7, vol. iii. 



p. 438, tig. (!. 



Dt'Knijifinn. — Shell discoiilal, soniewliat compressed, and vatlier widely uinbili- 

 cated ; greate.st thickness close to the umbilical margin, about four-iiiiitlis of the 

 diameter of the shell, height of outer whorl about three-sevenths of that diameter. 

 Whorls possibly si.\ or seven, l)ut in default of perfect adult specimens the numlwr 

 must for the present remain doubtful. Inclusion fully three-fourths. Umbilicus 

 about four-elevenths of the diameter of the shell in width, very deep, exposing all 

 the inner whorls, the margin subangular, sloping inwards, steep. Whorl semi- 

 elliptical in cross-section, slightly wider than high, indented to about three-eighths 

 of its height by the preceding whorl ; sides very slightly convex, merging in the 

 rounded periphery. 



Body-chamber occupying the whole of the last whorl. 



Huture-line as in PL XL, fig. 3. 



Test ornamented with fairly regular, not very prominent ribs, which are stronger 

 in the young shell than in the adult, in which they Ijecome almost obsolete ; they 

 form a gentle, backwardly directed curve on the sides of the shell, and are sharply 

 bent backwards upon the periphery. Constrictions appear at intervals, about six 

 being counted in a whorl ; their direction corresponds exactly with that of the ribs. 



Dlvicii.'i'iuiis. 



Tj'pe speciiiiou in Siiocinien from St. Dou- 

 the British l:i.i;li's, in the Wood- 

 Museum wardiiiu Museum, Cam- 

 (No. C. 2<JS). bridge (No. 139). 



Diameter of shell (Ijody-chamber, incom- 

 plete in Cambridge specimen) 97 nun. . 55 mui. 

 „ umbilicus (edge to edge) . 35 ,, . 20 ,, 

 „ ,, (suture to suture) . 30 „ . 17 ,, 

 Height of outer whorl . . 41 ,, . 21- ,, 

 ,, above preceding whorl (about) . 26 ,, . — ,, 

 Thickness at unil)ilical margin (about) . 41- „ . 26 ,, 



Al]iiiiti('s. — The I'elations of this species to I'rrici/chis FmiriU and to /'. rnhili- 

 farmis are referred to under the descrijjtions of these species.' The great di'pth 

 of the uml)ilicus and the comparative feel)leness of the ribbing, together with the 

 rounded foi-m of the [)eripliery, are its distinguishing features. 



Ri'inmirs. — As ivgards the form of the shell and the character of the ornaments, 



' P. Fuordi, i>. 141 ; P. roluliformis, p. 148. 



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