INVERTEBRATE PALAEONTOLOGY. 4(51 



long, with a serrated end, and a still smaller, narrow, oblique, nearly simple, 

 fifth lateral lobe. These additional smaller divisions at the umbilical margin, 

 together with the more obtuse subdivisions of its sinuses, as more correctly 

 made out in the tbregoinig cut, give the septa slightly more the aspect of 

 those of Phylloceras than as represented by our figure on plate 24. 



Some peculiarities, however, observed in a large distorted specimen of 

 this shell now before me, also seem to present additional reasons for doubting 

 its exact generic identity with Phyllocems. This specimen is nearly ten 

 inches in diameter, with apparently at least the whole outer volution non- 

 septate. It is accidentally compressed and otherwise distorted ; but I am 

 strongly impressed with the belief that its outer volution naturally made two 

 deflections from the regular curve of those within, much as seen in Ammo- 

 nites bullatus, d'Orbigny, though the shell is of course otherwise very differ- 

 ent from that species. This deflection, or departure, from the regular curve, 

 makes the outer volution much less deeply embracing than the inner, and the 

 umbilicus consequently much larger proportionally in the adult, than in the 

 young and medium-sized specimens. 



I would be more inclined to attribute this irregularity in the large spe- 

 cimen of this species mentioned above to accidental distortion, were it not 

 for the fact that the smaller individual figured on our plate 24 (see fig 3, «) 

 also gives some evidence of the commencement of a similar irregularity of 

 the curve of the outer volution, a part of which turn has been broken away. 

 This specimen, too, has been subjected to some distortion from compression ; 

 but it seems hardly possible that tins could have produced the deviation from 

 the regular curve of the inner volutions mentioned. At one time, this pecu- 

 liarity led me to suspect that this shell might really be a Scaphite ; but the 

 apparent repetition of the irregularity in the curve ^een in the larger speci- 

 men (only the two examples are known), apparently without the body volu- 

 tion becoming free, is unlike the deflections of the outer volution of that 

 genus, and, as above suggested, more like those seen in shells of the type 

 of Ammonites bullatus, to which group, however, our species certainly does 

 not belong. 



I have, therefore, only referred this species to Philloceras, rather as a 

 nearer approximation to its true position, than from a decided conviction that 

 it really belongs to that group; or, in other words, because it is brought by 

 its known characters much nearer that genus than to Ammonites as restricted 



