158 FIFTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



PLATE 2. 



Fig. 1. Orthis emacerata. Dorsal valve. 



Fig. 2. " " Interior of tlie ventral valve. 



Thirteenth Annual Report on the State Cabinet, page 121. 



Fig. 3. " " Interior of a ventral valve of the form or- 



dinarily referred to O. testudinaria. 



From the same geological position. 



Fig. 4. Orthis clttie. Dorsal view. 



Fig. 5. " " Interior of ventral valve. 



Fourteenth Annual Report on the State Cabinet, p. 90. 



Fig. 6-8. Orthis[?] ella. 



Thirteenth Ann. Report id. p. 121. = Trematospira? ella. 

 The specimens figured show the extremes of variation in number of plica- 

 tions, etc. The species is not an Orthis, but possesses characters belonging to 

 Trematospira, but with a more distinct area than has been observed in any 

 species of that genus; while there is no sinus upon the ventral valve. 



Fig. 9 - 11. Trematospira hirsuta. 



Fourteenth Annual Report on the State Cabinet, p. 101. 

 = Atrypa hirsuta. Tenth Ann. Report id. p. 128. 



Fig. 12 - 14. " " Dorsal, front, and profile views of 



a large individual, in which the mesial fold and sinus are strongly 

 developed. 



Fig. 15 & 16. *' " Interior of the ventral & dorsal valves. 



Fig. 17 - 25. Meristella? UNisuLCATA^r^tri/pa unisulcata : Conrad, 

 :r .- Annual Report of 1841. 



See Fourteenth Annual Report on the State Cabinet, p. 101. 

 Fig. 17 is a cardinal view of a well-preserved form from the Upper Helder- 

 berg limestone ; in which there is a ridge -like fold on the dorsal valve, parallel 

 with and close to the hinge-line or cardinal margin of the valve. In fig. 18, a 

 specimen from the Hamilton group, this fold is more oblique, rising from near 

 the beak, as shown in the figure, while there is a second fold on the side of the 

 shell. Fig. 19 is a specimen from the Upper Helderberg limestone of the West ; 

 in which the fold is sharp and clearly defined, slightly oblique, and inter- 

 mediate to the former two : the specimen is more gibbous than those from 

 the limestone of New-Tork*. Figs. 20 & 21 are ventral and dorsal views of 

 a large specimen from the limestone of New -York; Fig. 22, profile of the 

 same; Fig. 23, front view of the same. Fig. 24, interior of the dorsal valve, 

 showing a median septum, cardinal process, teeth, sockets, and bases of the 

 crura. Fig. 25, interior of ventral valve, showing the teeth and muscular 

 impression. 



These figures (24 & 25) are from specimens, before referred to, as furnished 

 through the kindness of Mr. S. S. Lyon, from the limestone of the Falls of 

 the Ohio. 



* For the present, and until farther investigation, I would propose to designate the Hamilton 

 jorm as M. unisulcata^ var. biplicata; and the western form as M. unisulcata^ var. uni- 

 plicata. 



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