Cephalapoda. g^. Solenoceras. 



Humboldtianus, Karst. Sp. (Ptychoceras), Gabb, 1861. N. 



Gren. JST. 



Mortoni, Meek & Hayden. Sp. (Ptychoceras), Gabb, 1861. Ne- 

 braska, a 



TOXOCERAS, d'Orb. 1841. 



annulare, d'Orb. P. F. 480, 118, 1-6. Fr. JV. 



Astierianum, d'Orb. Prod. 66. Fr. AT. 



bituberculatus (urn), d'Orb. P. F. 476, 116, 8-10. Fr. N. 

 Cornelianus, d'Orb. (ANCYLOCERAS), P. F. 484, 119, 5-9. 



Duvalianus (urn), d'Orb. P. F. 479, 117, 6-9. Fr. N. 



elegans, d'Orb. P. F. 477, 117, 1-5. Fr. N. 



Einericianum, d'Orb. P. F. 487, 120, 5-9. Fr. N. 

 gracilis, d'Orb. (Hamites), P. F. 488, 120, 10-12. 



Honnoratianus (urn), d'Orb. P. F. 483, 119, 1-4. Fr. N. 



Joubertianus (urn), d'Orb. Prod. 101. Fr. N. 



Moutonianus (urn), d'Orb. Prod. 101. Fr. N. 



nodosus (urn), d'Orb. Prod. 101. Fr. N. 



obliquatus (urn), d'Orb. P. F. 486, 120, 1-4. Fr. N. 



plicatilis (le), d'Orb. Prod. 101. Fr. N. 



Requienianus (urn), d'Orb. 474, 116, 1-7. Fr. N. 

 Royerianus (urn), d'Orb. P. F. 481, 118, 7-11. Fr. L. G. 



Varasensis (se), d'Orb. Prod. 102. Fr. N. 



TRIGONELLITES, Park. 1811.* (Aptychus, Yon Meyer, 1831.) 



Cheyennensis, M. & H., Sp. (Aptychus), Gabb, 1861. 

 crassus, Hebert, Sp. (Aptychus), Gabb, 1861. 

 fragilis, M. & H., Sp. (Aptychus), Gabb, 1861. 

 Gollevilliensis, Sharpe, Sp. (Aptychus), Gabb, 1861. 

 Icenicus, Sharpe, Sp. (Aptychus), Gabb, 1861. 

 insignis, Hebert, Sp. (Aptychus), Gabb, 1861. 

 leptophyllus, Sharpe, Sp. (Aptychus), Gabb, 1861. 

 obtusus, Hebert, Sp. (Aptychus), Gabb, 1861. 

 peramplus, Sharpe, Sp. (Aptychus), Gabb, 1861. 



dence is very slight. I have frequently examined the type of the genus, which 

 is also Morton's type of his species, and although, at the extremity of the frag- 

 ment there is a slight deflection, it always appeared to me to be only a thickened 

 lip or rib, such as occurs at intervals on other species in this family. The chan- 

 nel for receiving the older or smaller arm of the shell, is so deep as to render a 

 section across the mouth crescentic. 

 *' See note under APTYCHUS. 



