7117 



Class CEPHALOPODA. 



Order TF.TK.Mti; \N< II I AT A. 



Suborder NAUTILOIDKA. 







Family KNDOCERATIDJ 

 (Jenus PILOCERAS, Salter, 1859. 



I'M.OCKKAS NKWTON-WWCHRLLI, 8p. nOV. 

 PLATE XLVII. F108. !-. 



Two specimens preserved in a white chert indicate a small undescribed species 

 of this genus. The more complete of the two is obliquely fusiform, slightly arcuate 

 on the siphonal side, and bears sixteen septa which are very oblique on the upper 

 part but lose this obliquity toward the apex; the direction of the earliest septum is 

 nearly transverse. The obliquity of the later septa is so great that the last septum 

 exposed, in crossing the shell from the dorsal to the ventral side traverses the depth 

 of five air-chambers on their antisiphonal exposure. The length of this specimen 

 is 31 mm. and its width at the top measured along a suture, 21 ram; the transverse 

 diameter at the top, 17 mm; at the base 7 mm. All the air-chambers are deepest 

 at the antisiphonal edge. At the top of the specimen is the opening of a wide 

 siphonal cavity. A longitudinal section of the specimen along the axis of this 

 ravity shows some interesting points of structure. The mouth of the cavity is 

 broad at the top, covering nearly one-third of the entire diameter of the shell. Its 

 actual and relative diameter lessens, however, toward the apex. The position and 

 relative size of the sipho and the difference in the direction of the septa on the two 

 sides are shown in the accompanying figure. This cavity is not filled by a solid 

 accumulation of siliceous matter, but is more or less cavernous. The siphonal 

 walls, however, are encrusted and <li>tinrtly retained. It is very clearly evident 

 from this section that the septa are not coalesced with the siphonal wall (ton). The 

 edge of each septum lies close against, usually in actual contact with a thickened 



