204 PALJEOXTOLOGY OF NEW YORK. 



the siphuncle is gradually modified by a conical expansion of its tube, or by 

 a circumposed organic deposit. The base of the cone is sometimes excentric 

 with regard to the siphuncle, making a predominance of the expansion or 

 deposit on one side, as shown in figs. 8-11, pi. 113. 



Test and surface-markings unknown. 



Internal mould smooth, showing some traces of a transversely striate sur- 

 face. Suture line but slightly impressed on well-preserved specimens. 



One specimen has a length of twenty-seven mm., with diameters of 1.5 

 and .75 mm. at the two extremities respectively, and embraces twenty air- 

 chambers. Several fragments have been observed, belonging to larger indi- 

 viduals, but the dimensions given represent the usual siz". 



This minute and delicate species is remarkable for its small size, the great 

 depth of the air-chambers, the characters of the siphuncle, and the appearances 

 around the siphuncle at the anterior portion of each air-chamber. Specimens 

 are not uncommon in the soft shales along the east shore of Cayuga lake. 



Formation and locality. In the soft, black shales of the Hamilton group, at 

 Norton's Landing, Cayuga lake, N. Y. 



Section d. — Fwrnn hating the cone fluted. 



Orthoceras (Edipus, n. sp. 



PLATB8 WWII, FIG. 6; I. XXXII, BIO. 17. 



Tli is species is indicated from several fragments possessing characters distinc- 

 tive from 0. pmfundum and O. JEgea. The shell is large, straight, regularly 

 and rather rapidly enlarging. Transverse section circular. 



Chamber of habitation well developed. Air-chambers increasing in depth 

 with the diameter of the tube. Where the tube measures twenty-five mm. 

 in diameter the depth of the air-chambers is about six mm. 



Septa smooth, thin, having a concavity equal to an arc of 97°. Sutures 

 straight and horizontal. 



Siphuncle excentric, distant from the margins of the septa eleven ami 

 fourteen mm., as measured along the dorso-ventral diameter. Its diameter is 



