NATURAL SCIENCES OF PHILADELPHIA. 



185 



regarded in all cases, of even specific importance, since it is now well known 

 that in some instances the same species presents both these peculiarities, and 

 sometimes the whorls of one part of the spire are in contact, and in others dis- 

 connected, even in the same individual. 



Our specimens confirm Mr. Sharp's views, for although they are but mere 

 fragments, it is evident they are parts of spiral shells, presenting intermediate 

 gradations between forms with whorls barely in contact, and others in which 

 they are clearly disconnected. 



Mr. D'Orbigny describes the septa of the genus Helicoceras as being un- 

 symmetrical, like those of Turrilites, this, however, is not always the case in 

 species, the whorls of which make a very broad curve around a large umbilical 

 cavity, for in some of our specimens of this kind, the corresponding lobes on 

 opposite sides of the siphuncle, present scarcely the slightest inequality, and 

 in other instances seem to be as nearly symmetrical as in Hamites, or any of 

 the allied genera. 



Names formerly used. 



Hamites Mortoni, Hall & Meek. 1 



Helicoceras tenuicostatum, Meek & Hayden. j 

 Turrilites (Helicoceras) cochleatus, M. & H. 

 Ancyloceras? Nebrascensis, Meek & Hayden. 



Turrilites Nebrascensis, Meek & Hayden. 

 Ancyloceras ? Cheyennensis, Meek & Hayden. 



Turrilites Cheyennensis, Meek & Hayden. 

 Turrilites umbilicatus, Meek & Hayden. 

 Ammonites percarinatus, Hall & Meek, 



presents extremely different characters, at 

 various stages of its growth ; probably not 

 distinct from A. Woolgari, of Mantell. 

 Ammonites cordiformis. Meek & Hayden, 



probably identical with A. Cordatus, Sowerby. 

 Planorbis fragilis,* M. & H. (non Dunker.) 

 Planorbis subumbilicatus, Meek & Hayden. 

 Planorbis amplexus. Meek & Hayden. 

 Paludina Conradi, Meek & Hayden. 

 Paludina moltilineata, Meek & Hayden. 

 Paludina Leai, Meek & Hayden. 

 Paludina retusa, Meek & Mayden. 

 Paludina trochiformis, Meek & Hayden. 

 Turritella Moreauensis, Meek & Hayden. 

 Scalaria cerithiformis, Meek & Hayden. 

 Turbo Nebrascensis. Meek & Hayden. 

 Rostellaria biangulata. Meek & Hayden. 

 Fusus contortus. Meek & Hayden. 

 Buccinum ? vinculum, Hall k Meek. 

 Acteon attenuatus, Meek k Hayden. 

 Acteon concinnus, Hall & Meek, \ 



Avellana subglobosa, Meek & Hayden. j 

 Acteon subellipticus, Meek & Hayden. 

 Natica paludinjEformis,* Hall & Meek. 



(non N paludiniformis, D'Orbigny.) 

 Bulla subcylindrica,* Meek & Hayden. 

 Corbula ventricosa, Meek & Hayden. 

 Corbula Moreauensis, Meek & Hayden. 

 Cytherea tenuis. Hall & Meek. 

 Cytherea pelluclda, Meek Ik Hayden. 

 Cytherea Deweyi, Meek 8c Hayden. 

 Cytherea Owenana, Meek St Hayden. 

 Cytherea orbiculata, Meek & Hayden. 

 Cyclas Formosa, Meek & Hayden. 

 Cyclas fragilis, Meek & Hayden. 

 Cyclas subelliptica, Meek & Hayden. 

 Hettangia Americana, Meek & Hayden. 

 Nucula Evansi, Meek & Hayden. 

 Nucula scitula, Meek & Hayden. 

 Cucull^a Shumardi, Meek & Hayden. 

 Pectunculus Siouxensis, Hall & Meek. 

 Pectunculus subimbricatus, Meek & Hayden. 



Names here adopted. 



Helicoceras Mortoni. 

 Helicoceras cochleatum. 

 Helicoceras Nebrascense. 

 Helicoceras Cheyennense. 



Helicoceras umbilicatum. 



Planorris planoconvexus. 



Valvata subumbilicata. 



Helix (Polygyra) amplexus. 



Vivipara Conradi. 



vlvipara multilineata. 



Vivipara Leai. 



Vivipara retusa. 



Vivipara trochiformis. 



Cerithiopsis Moreauensis.' 



Turbonilla (Chemnitizia) cerithiformis. 



Margarita Nebrascensis. 



Aporrhais biangulatus. 



Pleurotoma contorta. 



Fusus vinculum. 



Solidulus attenuatus. 



Avellana concinna. 



Solidulus (Acteonina ?) subellipticus. 



Amadropsis paludiniformis. 



Bulla speciosa. 

 Ne^ra ventricosa. 

 Ne^ra Moreauensis. 

 Meretrix tenuis. 

 Meretrix pellucid a. 

 Meretrix Deweyi. 

 Meretrix Owenana. 

 Meretrix orbiculata. 

 Sph^erium formosum. 

 sph.erium fragile. 

 sph.erium subellipticum. 

 Tancredia Americana. 

 Leda Evansi. 



IiEDA SCITULA. 



Cucull^a fibrosa, Sowerby. 

 AXW.EA Siouxensis. 

 AXIN.SA subimbricata. 



I860.] 



*The names followed by an asterisk, were pre-occupied. 



