110 CARBONIFEROUS CEPHALOPODA OP IRELAND. 



of any specific characters common to the two species. Sowerby's species, with 

 its wide umbilicus, nuraei'ons whorls, and sutures with sharply bent sinus, can 

 have no affinities with a shell of the structure of P. oxystomum. 



It has already been pointed out by de Koninck ' that the species referred to 

 the present one by H. Trautschold - has no affinities with it. This species of 

 Trautschold, to which de Koninck has given the name Nautilus Bouillieri (loc. cit.), 

 has since been figured by M. Tzwetaev (loc. cit.). The form of the sutures, which 

 recalls that of Hercoglossa, is quite anomalous among the older palasozoic nautiloids. 

 They are strongly and abruptly bent forwards along the margin of the umbilicus, 

 and again bent, but in a wider curve and in the contrary direction, in the middle 

 of the sides. The acute form of the periphery and the generally compressed 

 habit of the shell are, indeed, the only features in which N. Ronillieri^ resembles 

 P. oxystornvm. The two species are further distinguished by the fact that the 

 umbilicus in the former is much smaller than in the latter. 



Bemarlcs. — If the figure given by de Koninck in his * Calcaire Carbonifere,' 

 pt. l.pl. xvii, were correct, it would lead to the supposition that the Belgian species 

 of Phacoceras was not identical with the one figured and described by Phillips 

 under the name of P. oxystomum. De Koninck's figure represents a species with 

 an umbilicus relatively much smaller than that of the last named. The figure 

 given by de Koninck in his ' Description des Animaux Fossiles,' etc., pi. xlix, is 

 much more accurate in this i-espect; both give a view of the inner whorls, the 

 importance of which, from the classificatory point of view, has been well pointed 

 out by Hyatt.* It is on the ground that the young have the form and proportions 

 of Dhcitoceras that he gave Phacoceras the temporary place here assigned to it ; 

 but it is evident that further investigations will be necessary before the question 

 of the true affinities of this singular genus can be solved. It is, however, a rare 

 fossil. 



It is unfortunate that the only specimen accessible to me for purposes of 

 description and representation in the accompanying plate (PL XXVIII) is not 

 localised. The occurrence of the species in Ireland is, however, well authenti- 

 cated, Phillips and Griffith (in M'Coy's ' Synopsis ') both referring to it ; the 

 former as occurring at Florence Court, near Enniskillen, the latter at Drumscraw 



' " Faune Calf. Carb. Belgique " (' Aud. Mus. lioy. d'Hist. jN'at. Belgique,' sor. Palaeoiit., torn, 

 ii), pt. 1, p. 124. 



- 'Nouv. Mem. Soc. Imp. Nat. Moscou,' 1S74, torn, siii, p. 304, pi. ssx, fig. 7. See also M. 

 Tzwetaev, ' Jlem. Com. Geol. St. Petersbourg,' 1888 vol., No. 3, pi. vi, figs. 33, 34. 



3 Assigned by Hyatt to his genus Stenopoceras, " Carboniferous Ceplialopods." ' Geological 

 Survey of Texas, Fourth Annual Report,' 1892, p. 446. 



■* "Carboniferous Cephalopods." Second paper. 'Geological Survey of Texas, Fourth Annual 

 Report,' 1892, p. 438. 



I 



