274 PALEONTOLOGY OF NEW JEESEY. 



third of its length, but is again abruptly expanded just behind the aperture; 

 the opening itself having been circular and smaller than the tube behind it. 

 Surface of the cast finely and closely annulated, the annulations having a 

 direction just perceptibly backward in crossing from the inner to the con- 

 vex surface, and count just eight annulations in the space of one-fourth of 

 an inch on the largest part of the outer tube ; on the inner concave face the 

 annulations are somewhat finer, as many of them are doubled at the edge 

 of the concavity, giving in the aggregate nearly one-third more annulations 

 within a given distance. On the back of the cast two lines of minute nodes, 

 marking the crests of the annulations for a short distance behind the aper- 

 ture, are faintly perceptible under a good magnifier. 



On the posterior extremity of the outer chamber the lobation of the 

 last septum is obscurely marked, showing a moderately strong dorsal lobe, 

 with a larger lateral lobe on each side, while a large bilateral sinus has 

 occupied each edge with a lobe on each ventral side, and a very small ven- 

 tral lobe on the inner surface. The details of the lobes and sinuosities are, 

 however, too badly defined to be traced. The surface of the shell of the 

 septum is beautifully iridescent, and slight traces of iridescence are percepti- 

 ble on other parts of the cast. 



The specimen here used and figiu-ed is Morton's type of the species, 

 and is also that used by Mr. Conrad for the type of his genus Solenoceras. 

 As yet no other has been observed so far as I can ascertain. It diff'ers 

 fi-om the species described as Ptyclioceras Mortoni by F. B. Meek in his 

 Vert. Paleont. U. S. Geol. Survey of the Terr., p. 412, PI. xx. Fig. 4, in 

 the direction of the transverse ridges which are more direct, and possibly 

 in their being somewhat finer and more regular ; on the whole, however, 

 it is very similar. From P. Meekanum Whitf, of the Black Hills report, it 

 differs much more widely in that that species is more coarsely annulated, 

 and the annulation much more acute and oblique. 



Formation and locality: The type specimen, as stated under the original 

 description by Dr. Morton, is from the Lower Green Marls, at the Deep 

 Cut of the Chesapeake and Delaware Canal, Delaware. It is very 

 probable, however, that by careful observation it might be discovered in 

 the Lower Marls in New Jersey. The specimen is in the collection Acad. 

 Nat. Sci., Phila. 



