POTERIOCERAS LATISEPTATUM. 45 



shorter and more inflated form than that to which de Koninck has given the same 

 specific name. 



De Koninck's allocation of P. fuslfurmc to Gomphoceras was unfortunate 

 considering that not only is the aperture simple in Poterioceras, but the form of 

 the shell is different from the latter, even allowing for the absence of the apical 

 part in Gomphoceras, which gives to this form a stump}^ and, if I ma}^ so express 

 it, ungraceful outline. The complicated, multilobate aperture of Gomphoceras 

 indicates structures in at least the oral parts of the animal which would certaiul}' 

 be regarded as of generic importance in any living form, and it is therefore witli 

 no great latitude that we assign a distinct generic position to the fossil. 



Localities. — St. Doulagh's, county of DubHn ; Miliicent (Clane), county of 

 Kildare (M'Coy, Haughton) ; Kildare, (exact locality not stated) (Phillips) ; Little 

 Island, near Cork (Dublin Museum of Science and Art). 



PoTERiiiCERAS LATisEfTATrji, sp. uov. Plate XVI. 



Description. — Shell of moderate size, fusiform, slender, inflated, the inflation 

 being most prominent dorso-ventrally, and, influenced by the curvature of the 

 shell, a little higher on the ventral than on the dorsal aspect (PI. XVI, fig. 2 a). 

 Section nearly circular when uncompressed. The shell tapers gradually from the 

 very acute apex, the inflation beginning at about the mid-length, becoming 

 contracted in diameter towards the aperture. The apex has a central, very 

 shallow pit, surrounded by a thickened rim ; in the centre of the pit there is a 

 circular spot representing the orifice of the siphuncle through which the latter 

 passed out of the protoconch or embryonic chamber. The diameter of the apex 

 is 2 mm. (PI. XVI, fig. 2 a). The body-chamber (partly exposed in some of the 

 specimens by the removal of the test) has an undulating outline at the base, but 

 in a general sense it is liorizontal. 



The septa are comparatively distant, there being seven in a length of 45 mm. 

 in this species, against ten in P.fusiforme in the same length. The last two or 

 three chambers are very shallow in some specimens (PI. XVI, fig. 4). The 

 course of the sutures is slightly oblique on the lateral areas of the shell (PI. XVI, 



fig- 3 a). 



The siphuncle is situated near the convex margin ; fig. 4 shows its position, 

 which is seen to become gradiuilly more nearly central as the shell grows. It has, 

 unfortunately, not been cut quite through the centre in the specimen figured, 

 consequently the segments do not appear to completely fill up the space they 

 occupy between the septa, and owing to this also they have an oval instead of a 

 nearly circular form. 



