1856.] 



81 



Anodonta WaMamatsnsis, Lea. Tr. Am. P. S.v. 6, p. 78.=.4. iriangulata, Trask. 

 A. roliindovata, Trask. From Sacramento River. 



Anodonta angulata. Lea. Tr. Am. P. S. v. 6, p. 97.=.4. feminalis, Gould. A. 

 Randall), Trask. From upper San Joaquin. 



Helix Oreffonensis, Lea. Trans. Am. P. S. v. 6, p. 100. Point Cypress, Monterey 

 County. 



Jlelix Nickliniana, Lea. Trans. Am. P. S. v. 6, p. 100. Tomales Bay and 

 , Deadman's Island. 



Helix CaUforniensis, Lea. Trans. Am. P. S. v. 6, p. 99. Point Cypress, 

 Monterey County. 



Lt/mneea exigua, Lea. Trans. Am. P. S. t. 9, obs. v. 3. San Antonio Arroya. 



Lt/mncea pallida, Adams. Journal Boston Nat. Hist. See. v. 3. San Antonio 

 Arroj'a. 



Physa heterosfropha, Say. Nicholson's Ency. Am. Edition. Los Angeles. 



Melania occata, Hinds. Voy. of the Sulphur, pi. 15, f. 5. Sacramento River. 



3Ielania scminalis, (Faludina, Hinds.) Voy. Sulphur, pi. 16, fig. 22. Sacra- 

 mento River. 



Planorbis (rivoli.s, Say. Nicholson's Ency. Am. Ed. Hern Lake. Slightly 

 varies from the Michigan specimens. 



Planorbis ammon, Gould. Proc. Boston Soc. Nat. Hist. v. 5, p. 129. Lagoons, 

 Sacramento Valley. 



Descriptions of twenty-eight new species of AcephaJa and one Gasteropod, from the 

 Cretaceous formations of Nebraska Territory. 



By F. B. Meek and F. V. Hayden, M. D. 



Pholadomya undata. Shell oval or ovate, moderately ventricose, anterior 

 end rounded, posterior extremity rounded chiefly from below, cardinal border 

 nearly straight ; base somewhat broadly curved ; beaks rather elevated, incurved, 

 placed between the centre and the anterior end ; surface (of cast) ornamented 

 by numerous, regular, distinct, concentric undulations, which are crossed by 

 much smaller radiating costse, scarcely marked in the depressions between. 

 Length about one inch. 



As we have not seen the hinge of this species, we refer it with doubt to the 

 above genus. The radiating costaj are about equal, the spaces between, and in 

 consequence of being marked only on the concentric undulations, and not in 

 the intermediate depressions, furnish a character by which even fragments of 

 the species may be at once identified. 



Locality and position. Mouth of Judith River, in a sandstone supposed to be 

 same as No. 1 of the series. 



GoNiOMYA AMERICANA. Our Specimens of this interesting shell are too imper- 

 fect to give a clear idea of its form, though the direction of the lines of growth 

 indicate an oblong or very narrow oval outline, with a narrowly rounded ante- 

 rior and subtruncate posterior. Laterally the valves must have been considerably 

 compressed. The beaks are small, not much elevated, and placed in advance 

 of the centre. On the two extremities the costse, which are quite distinct, tra- 

 verse the shell obliquely backwards from near the hinge to the base, while those 

 originating immediately in front and behind the beaks, converge and meet at 

 various distances down the sides of the shell, so as to form arched or convex 

 angles of from 20 to 30. Surface ornamented bj' fine irregular lines of growth, 

 crossed by regular, equi-distant, radiating rows of minute transparent granules, 

 placed at regular distances from each other. These granules are so small as to 

 be scarcely visible without the aid of a strong magnifier, under which they look 

 like minute drops of melted amber. 



In its surface markings this species resembles G. Dubois of Prof. Agassiz, 

 (^Eludes critiques sur les Moliusques fossiles, tab. 1.) but in our species the con- 

 verging costa; continue to meet at the same acute angles as far as they can be 

 traced towards the points of the beaks, while on the beaks of G. Dubois and 



