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 bodj^-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. Xeither septa nor siphuncle are seen in the specimen 

 before me. 



Dimensions. 



Sci. and Art Mus., Dublin. 

 M-Coy's type, " Griffitli Coll." 



Diameter of shell . . . .52 mm. 



„ umbilicus (from edge to edge) . 30 ,, 



,, ,, (from suture to suture) . 19 ,, 



Height of outer whorl (dorso-ventral) . . 21 ,, 



Thickness at umbilical margin . . . 28 ,, 



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 3'oung specimen of V. cariuiferns, 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 Hj'att also the 

 developmental historj' of the two groups (Coloceras and Veiii nautilus) is distinct. 

 Comparing the present species with 0. bistrialis (described below), Hyatt says 

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

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

 specimens [of G. Goj/aimm^ in the Museum of Comparative Zoology (Cambridge, 

 Mass.), which show that this and C. glolatus, de Kon., as figured in the ' Calc. 

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

 may be so, but it must be understood that the C. globatus of de Koninck is not 

 that of J. de C. Sowerb}'. 



lieiitarls. — 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 Coloceras 

 Goyanum to Vestinautilus cariniferin^. 



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

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



