278 PALEONTOLOGY OF NEW YORK. 



Section b. — Slender forms. 

 Orthoceras Marcellense. 



PI III - WXVIll, KIGS. 4, 5, (I. 7,8; I.XXX1II, FIGS. 1-10,12; (XIII, FIG. IS. 



Marcellus orthooara, Yamxkm. Geolog. Bnrv. of N. V. : Report oftbe Third District, p. 147. 1842. 

 Otlkrrtrtn tjgnUi Ttwtimi Dunker and von Myer. PalaxMtogi-apbica, Dritter Band, ;s. Lieferumr, p. 165, 



pl. 20. 18r>3. 

 MaiiellrtisL* (Vamxkm), Ham. Thirteenth Rap N. Y. State Cab. Nat. Hist . p. 106. I860. 

 " typwm ( S t int * ™ ), Hall, In part. Illustrations of Devonian PmsUb: Cephalopoda Explanation 



of pl. 38. 1876. 

 " . Marcelleiise, Va.m-xem. Catalogue Am. Pal. Fossils, S. A. Millek, p. 175. 1877. 



Shell straight, extremely elongate, very regularly and gradually expanding 

 from the apex to the aperture. Transverse section circular Apical angle 

 varying from six to eight degrees in specimens apparently undisturbed by 

 compression. Initial extremity very acute; the remaining characters are 

 obscure. 



Chamber of habitation well developed, having a length of about four times 

 the diameter at the last septum, regularly expanding to a point near the 

 aperture where there is a very gentle constriction. Air-chambers numerous, 

 about sixty in the length of the tube ; regularly increasing in depth from 

 the apex to the outer chamber, having a depth of about ten mm. near the 

 grand chamber. 



Septa thin, with a variable concavity, usually equal to an arc of about 

 115°. Sutures straight, or sometimes slightly oblique. On the convex side 

 of the septa, near the chamber of habitation, there is a simple areola sur- 

 rounding the insertion of the siphuncle. Towards the apex this areolar 

 marking is much thickened and elevated, with a prominent process, extending 

 to the ventrum (pl. 83, figs. 4, 5); the whole having a furrowed and pitted 

 margin, and surrounded by radiating, vascular markings over the septa (pl. 

 83, 6gs. 6, 7). 



The process, extending to the ventral margin, is continued, as shown in 

 the cast of the interior of the tube, along the ventral walls of the air-cham- 

 bers, and sometimes along a portion of the grand chamber, as a carina. 

 Sometimes this central line has a similar, smaller carina on each side, 



