CCELOXAUl'ILUS PLANOTERGATUS. 53 



ridges, or would show tliem so faintly as to cause them perhaps to be overlooked. 

 A specimen from St. Doulagh's, which came under my notice (it is not now 

 accessible to me), may prove to be a distinct species ; it is more rapidly tapering 

 and more slender, and has a stronger curvature than T. jinrnrloxinim. On com- 

 paring the curvature of the two species (assuming for the moment that they are 

 distinct) it is found that in the St. Doulagh's shell the greatest curvature upon a 

 chord of 70 mm. subtending the concave side is 2o mm. ; while in a specimen of 

 T. paradoxicum from Clane, now before me (PI. XVIII, figs. 3 a, h), the greatest 

 curvature, upon a chord of 70 mm. subtending the concave side, is 6 mm., or 

 about one-fourth the above amount — a very considerable discrepancy. 



A fragment from Clane in the Grainger Collection shows narrow bands of 

 colour of a dark brown hue and of a zigzag pattern, curving a little as they 

 approach the dorsal keel (PI. XVIII, fig. 5). 



It is unfortunate that the specimen mentioned by M'Coy as exhibiting the 

 incurved apical extremity was contained in a private collection, that of the Rev. 

 Dr. Sirr. The prospect of tracing this collection is now, after such a long lapse 

 of years, hopeless, and we must trust to renewed search for the completion of our 

 information regarding the structure of Trigonoceras. My friend Mr. Joseph 

 Wright, F.G.S., of Belfast, informs me that he saw, many years ago, two 

 specimens of Trigonoceras in the Museum of Science and Art, Dublin, each with 

 the apex preserved, as described by M'Co}'. These also have long since dis- 

 appeared. It is satisfactory, however, to have M'Coy's observation confirmed by 

 so competent an observer. 



Localities. — Clane, county of Kildare; Rathkeale and Doohyle (near Rath- 

 keale), count V of Limerick; St. Doulagh's, county of Dublin. 



Genus CiEi.oXAUTiLUS, Vooril, 1891 (emend. Hi/aff, 189o). 



Gl.'OUP OF C(EL0.V.\nTII,US PLANOIKHfiATCrS. 



a. CfEr.ONAUTiLfs PLANOTERGATUS, F. M'Co]i, sp. Plate XIX, figs. 1 o, h, 2 a — c. 



1844. \actii,us (DfsciTEs) plvxotkrgatps, F. M'Coi/. Synop. Carb. Foss. 



Ireland, p. 18, pi. ii, fig. 2. 

 18C0. DisciTEs pLWOTKitajLtus, B. Ch-ijith. Journ. Geol. Soc. Dublin, vol. ix, 



p. 50. 

 1878. Xautii.cs pi.anotkrc.vtus, L. G. de Koninck. Faune Calc. Carb. 



Belgique (Ann. Mus. Eoj. d'Hist. Xat. 

 Belgiqiie, torn, ii), pt. 1, p. 117, pi. x.Tvi, 

 figs. 1-3. 



