Ac/r Sjicrii'^ of Fo^slh fi'oiii OhUi. "io.") 



suture-line distinct, but not niargineil by a flattening of the upper edge of 

 the succeeding volution. Aperture elongate, slightly angular at the base 

 and pointed above. Surface of the volutions marked by a large number of 

 distinct vertical striae, which are more numerous and slightlj^ tiner on the 

 body volution than above, and are so nearly destitute of sigmoid curvature 

 as to appear vertical until closely examined. 



The small bize of the shell, the nearly vertical lines, and the 

 unequally expanding volutions, arc distinguishing features ; the 

 latter character, howevei', ap])ears to vary a little in degree on 

 some of the specimens. It will be readily distinguished from 

 the young shells of L. Haniiltanue, which occurs in the same 

 rock, by the number of volutions and the slender form. 



Foriiiativn and Locality. — In the white cherty layers of the 

 Uliper Helderberg limestone, near Duljlin, Ohio. 



CEPHALOPODA. 



Trematoceras, u. geu. 



A straight, obconical, cephalopodous shell, presenting the characteristics 

 of an Orthoceras, so far as the appearance of the tube, septa and siphuncle 

 is concerned ; but with the additional feature of a line of elongated, raised 

 tubercles along one side of the shell, which have formed perforations 

 at certain stages of growth, probably confined to the outer chamber as 

 openings, which were closed as the animal extended the shell, and before 

 the septa opposite them were formed. Type, T. Ohioense. 



The shell for which the above generic name is proposed olfers 

 an entirely novel feature among the Orthoceratida?. The line 

 of nodes seen on the cast of the shell is entirely different from 

 anything pertaining to the ornamentation of the shell, and pre- 

 sents the same aj)pearance as would the partially filled perfora- 

 tions of a Haliotis, or like those shown on the back of species of 

 Bucania, and those on which the genus Tremanotus was founded; 

 neither is it a feature at all dependent upon the position of the 

 siphon or directly connected with it ; for in the specimen used 

 the siphon is slightly excentric, on the opposite side of the tube 

 from the nodes. Its position would thus indicate that it was 

 a feature pertaining to the dorsal lij) of the shell, corresponding 

 to the sinus seen in the lip of many other genera. Taking this 

 view of it, it would appear to indicate the existence of a deep, 

 narrow notch, with raised margins, in the lip of the shell at 

 stated periods, beyond which the shell was again united for a 



