CEPHALOPODA. 371 



Cyrtoceras .emulum, n. sp. 



PLATES XCVII, FIGS. 1-9 ; XCVIII, FIGS. 3, 4. 



Shell slender, curved, making more than one-fourth of one volution. For a 

 considerable distance back of the aperture the tube is but slightly arcuate, 

 and becomes more curved toward the apex. Transverse section broadly oval 

 or subcircular. Tube regularly and very gradually enlarging from the apex 

 to the aperture, and without special contraction or expansion. Apical angle 

 about 6°. 



The extent of the chamber of habitation has not been observed. The 

 crenulations show, as obscure longitudinal ridges and striae, over the internal 

 mould of the walls of the air-chambers. Aperture entire, with a sinus in 

 the ventral margin having a width equal to about twice the depth. 



Air-chambers having a depth of seven mm., but showing considerable 

 irregularity in different portions of the tube, and in different individuals. 

 Septa smooth, with a concavity greater than the depth of the air-chambers. 

 Sutures straight and horizontal. 



Siphuncle small, close to the ventral side, often exposed in the process of 

 weathering. 



Test thin, having a thickness of about .5 mm. on the grand chamber. 

 Surface marked by irregular, lamellose lines of growth. Tube ornamented 

 with somewhat irregular, numerous, sharp, foliate expansions of the test, 

 slightly inclining toward the aperture, and projecting about two mm. above 

 the general surface of the test. The distance between two ridges varies 

 in different specimens from two to three mm. Sinus sharp, deep, affecting 

 the surface striae and ornaments, together with the annulations of the internal 

 mould. 



Internal mould nearly smooth, but preserving traces of the crenulations 

 and the external ornaments and markings of the test. Sutures moderately 

 impressed. 



The largest fragment observed has a length of about 185 mm., with a 

 diameter of thirty-two mm. at the aperture, and shows but a very gradual 



