PERICYCLUS SUBPLICATILIS. 



14:5 



broadly convex, imperfectly defined ; sides feebly convex, somewhat flattened near 

 the imibilical margin ; umbilical zone narrow, well defined, nearly perpendicular 

 to the plane of symmetry of the shell. 



" Body-chamber occupying the whole of the last whorl ; aperture not seen, 

 but, judging by the growth-lines and ornaments, the peristome probably nearly 

 straight on the lateral area, and with a deep and broad hyponomic sinus. 

 Chambers [shallow] ; suture-line as in [PI. XXXVIII, fig. 2]. 



" Test ornamented with feeble, somewhat inequidistant ribs, which, arising at 

 the umbilical margin, pass thence obliquely backward as far as the margin of the 

 periphery, where they bend somewhat abruptly backward, and form on the 

 periphery a deep and wide hyponomic sinus ; on the periphery the ribs become 

 nearly equidistant, fairly coarse, and separated by interspaces of about their own 

 width ; the ornaments gradually disappear on the outer whorl, those on the lateral 

 area disappearing first, and the ribs on the periphery at about the middle of the 

 last whorl. The whole surface of the test with very fine growth-lines." 



Dimensions. 



Diameter of shell 



„ umbilicus (edge to edge) 



„ „ (suture to suture) 



Height of outer whorl 



„ above preceding whorl about 



Thickness of shell at umbilical margin 



Cast of type specimen, 



in Museiun of 



Science and Art, 



Dublin. 



11 '3* 5 mm.^ 

 40 

 33 



43-5 „ 



55 



35 



44 



Specimen from St. 



Doulagh's, in the 



Woodwardian Musenni, 



Cambridge. 



55 



120 

 45 

 37 

 50 



43 



mm. 



Affinities. — Mr. Crick recognised the close resemblance in the ornamentation of 

 the present species to that of Goniatites plicatilis, de Kon.,^ which undoubtedly 

 exists, but the two species diifer widely in form. P. plicatilis ^ has a much more 

 inflated and thicker shell than P. suhplicatilis, and the umbilicus is more 

 cavernous in form and has steeper sides than the latter. More complete material 

 has convinced me that in the aggregate of characters P. Foordi is the most nearly 



' This specimen has beeu broken across and the fissure filled with calcite, so that the diameter of 

 the shell and the height of the last whorl appear to be greater than they really are ; the diameter 

 appears to be 122 mm., and the height of the outer whorl 555 mm. (Foot-note in Mr. Crick's 

 description of this species, loc. cit., p. 444, — to which may be added that the interposed vein of calcite 

 referred to, by adding to its length, gives the shell an elliptical shape.) 



- " Sur quelques Cephalopodes nouveaux du calcaire carbonifere de I'lrlande," 'Ann. Soc. geol. 

 de Belgique,' vol. ix, Memoires, 1881, p. 55, pi. v, figs. 3, 4. 



•' This species will be described and figured later on in this Monograph. 



22 



