M'Coy's type, " 



GlriffitU Coll. 



. 52 



mm. 



. 30 



5J 



. 19 



J» 



. 21 



J> 



. 28 



J5 



114 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



partly filled with matrix in the unique specimen now under description. The 

 umbilicus is bordered up to the base of the body-chamber by a sharp keel, which 

 completely disappears upon the body-chamber. The whorls overlap to the edge 

 of the keel, which is thus concealed until the last whorl releases itself from its 

 contact with the penultimate one. The periphery is rather broadly rounded, and 

 presents longitudinally three rather ill-defined zones. The aperture has a deep 

 hyponomic sinus. The body-chamber occupies about one-half of the last whorl. 

 The test is smooth. Neither septa nor siphuncle are seen in the specimen 

 before me. 



Dimensions. 



Sci. and Art Mus., Dublin. 



] 



Diameter of shell 



,, umbilicus (from edge to edge) 



,, ,, (from suture to suture) 



Height of outer whorl (dorso-ventral) 

 Thickness at umbilical margin 



Affinities. — There is ample justification for Hyatt's observation (loc. cit., p. 449) 

 as to the resemblance of the shells included in the group Coloceras to those of 

 Vestinautilus. At first sight there seems little of consequence to separate M'Coy's 

 type from a young specimen of V. cariniferns, but a closer comparison shows that 

 the latter has more numerous whorls and a proportionally wider umbilicus than 

 the former, as already remarked by M'Coy. According to Hyatt also the 

 developmental history of the two groups {Coloceras and Vestinautilus) is distinct. 

 Comparing the present species with C. bistrialis (described below), Hyatt says 

 that the former is a more slender aud less involute shell than the latter, and the 

 longitudinal ridges are not so persistent. He adds that " there are two good 

 specimens [of G. Goyanum'\ in the Museum of Comparative Zoology (Cambridge, 

 Mass.), which show that this aud 0. glohatus, de Kon., as figured in the ' Calc. 

 Carb.' (loc. cit.) [PI. XXXI, figs. la,h (not 1 c—e)'], are probably identical." This 

 may be so, but it must be understood that the G. glohatus of de Koniuck is not 

 that of J. de C. Sowerby. 



Hemarlcs. — The figure of the type specimen (the only one extant) is reversed 

 in the ' Synopsis ; ' it is represented in its natural aspect in the figure I have 

 given of it (PI. XXX, fig. 3). If this figure be compared with those on PI. XXIII, 

 numbered 1 and 2, it will be seen how close is the general resemblance of Goloceras 

 Goyanum to Vestinautilus cariniferus. 



Localities. — Kilmallock, near Limerick (M'Coy's type) ; BallydufF, near Dun- 

 garvan, county of Waterford (Jide Sir R. Griffith). 



