PLATK XC. 



Orthockr\8 Demus. 



I'ase 311. 



FiiT. 1. A ch»mbepeil frafrnient cihowiiijf the depth of the air-chamhei-s. The specimen does not preserve 

 any ii<lilitioiial cbai'aRtei'9, and is i-eferi'ed to the sjiecies with fiome hesitation. In the arena- 

 ceous shales »t Pliilipxhurgh, N. Y. 



Fig. 4. k fi-ajfmeiil fetaining- its noi-nial pi-<i|>ortions, and showing the characters of the 8|>ecie8. Chemung 

 group. CatcfuliUa ank, Itliaca, N. Y. 



Fig. 5. A small fra(rni»'iit in which the lube has been filled with irt)n pyrites, and the characters obscured. 

 Chemung group. Ithaia, N. Y. 



Orthockras PCLOIDUM. 



PlIKO SIO. 



Fig. 2. An individual retaining the chamber of habitiilion nearly entire, jiiid eleven of the attached air- 

 chainlH-'rF, (showing the enlargement of the tube and the distiiiice between the septa. Several 

 fragments of the test are adhei ing to the internal mould of the tube. Chemung group. Casca- 

 diila creek, Ithaca, iV. Y. 



Fig. 3. A jwrtion of a larger inilividual somewhat compressed, giving curvature and obliquity to the septal 

 sutures. Chemung group. Ithaca, N. Y. 



Orthoceras Leander. 



Vugu 309. 

 Rg. 6. A fragment somewhat compres.seil at the lower extremity, and showing the siphuncle as exposed 



from weathering. Chemung grouji South of Itliaca, N. Y. 

 Pig. 7. A clianiber of habitation and ten attached aii'-chunibers. 

 Fig. 8. An individual nearly entire, showing the rapid enlargement of the tutie and the characters of the 



chauil)er of habitation, with the slight expansion and constrii:tion of the tube at the aperture. 



Upper Chemung sandstone. Warren, Painxylvania. 



Orthoceras palmatum. 



Page 312. 

 Fig. 9. Lateral view of a fragment showing the depth of the air-chambers and enlargement of the tube. 



The ventral side of the specimen shows a longitudinal carina along the cast of the walls of the 



air-chambers. 

 Pig. 10. A septum of the preceding, snowing the size and position of the siphuncle with the raised areola 



arouml its insertion, and the i)alniate ornamentation extending to the ventral side of the tube. 



Chemung group. Southern New York. 



Cyrtoceras? Hector. 



PageSU. 



Fig. 11. A frngnient preserving the greater portion of the chamber of habitation, with several attached 

 shallow air-ihambei-s, showing a slight contraction of tlie tube at the aperture. Traces of Bne 

 stris of growth shown on the specimen are not repi-e.'!ente<l. Chemung group. Warren, Peima. 



Fig. 12. Another fragment showing deeper ;vir-cha;nl>er8. Chemung group. Ne.ir Olean, N. Y. 



Fig. 13 id. An opiM>8ile view, showing the curvature and obliquity of the suture lines. 



Pig. 14 id. A lateral view, showing a greater irregularity in the curvature and direction of the sutures. 



Fig. Ifi. An outline showing the transverse section of the tube. 



Orthoceras pertextum. 



i'UKK 314. 



Rg. 16. A fragment without evidences of septa, and showing the character and frequency of the annula- 

 tions. The surface-mai-kings are shown over the entire surface of the tube. Chemung gioup. 

 lUiaca, N. Y. 



Pig. 17. An enlargement of a portion of the surface of the preceding, showing the crenulated character of 

 the striffi. 



