PLATE XXV— Coiitimied. 



TnoVlJOVERAS AiNEAS* HaLL. . 

 Fig. 16. Vie^- of the upjier surface of the specimen described. 



Trochoceras {Gyroceras) bannisteri. Winch, d- Mar, 



Pase 403. 



Fig. 17. View of the specimen taken fiom a gutta-percha cast, of the umbihcal side showing it 

 to be a dextral species. 



Orthoceras abi\'0R3ie, Hall. 



Page 413. 

 Fig. 18. Transverse section of a specimen, showing the ramifying pi-ocesses within the siphuncle. 



LiCHAS OB\'ius, Hall. 



Page 444. 



Fig. 19. View of the glabella and lateral lobes of a specimen from the Niagai'a limestone at 

 Lyons, Iowa. 



i- 



Ltchas pugnax. Winch, cf- Mar. 



Page 424. 



Fig. 20. 'ilie pygidium of this species, from the same sjiccimen as the figure by jMessrs. Winchell 

 and Marcj', omitting the thoracic segments. Collection of Pi-of. Marcy. 



Bronte US acamas. Hall. 



Page 423. 



Fig 21. View of a small pygidium of this species. This figure is from the originiU of Bronteus 

 occasvs, W. & M. 



JlyLAJNlS AR.UATUS, HaLL. 

 Page 418. 



Fig. 22. A pj-gidium of this species, enlarged to two diameters, from a specimen loaned by 

 Prof. Winchell. The specimen shows a broad oval impression on each side of the 

 median line and anterior to the middle. Similar marks have been observed on other 

 specimens, and the}' may have been the areas of muscular attachment. 



* Trochoceras a'lieas, vor. up. — Shell sinistral, eln.sely coiled, volutions somewhat rapidly increasing in size, llat- 

 tened above and rounded (ui the dor.suni. the inner ones not projecting above the outer; number of volutions 

 undetennined. Septa numerous, about lour i^i a distance equal to the greatest diameter of those measured, 

 moderately concave, but appearing more deeply so from the flattening of the I'olution; strongly arcluug forwards 

 on the back, and less strongly on the ventral side. 



.^urtace uiarked by moderately sharp undulations which are directed backwai'ds from the inner to the outer 

 sides of the ^'olution. and arranged a little more closely than the septa, eleven of the latter eqiuiling thirteen of 

 the former on the dorsal niargin. 



This species differs from T. coatatinti, the only other sinistral species occurring in the same association, in the 

 flattening of the upper side ; the coucenh-ic undulations are finer than any other except T. Hmmisteri, from 

 which it differs in tbe flattened dorsum. ■ 



Formation and focniitj/. — In rocks of the Niagara gi-oup. at Lyons. Iowa. The specimen was received from Dr 

 Farnsworth. 



