118 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



As suggested in the paper above cited, it was probably an internal cast 

 of this species from which tig. 9, tab. 7, of Dr. Owen's Report of the Geol. 

 Survey of Wisconsin, Iowa, and Minnesota was drawn, though no specific 

 name was there proposed for it. 



Locality and position. — This species seems not to have an extensive 

 vertical or geological range. The specimens first described by Professor 

 Hall and the writer were collected by Dr. Hayden and myself at Sage Creek, 

 in upper part of the Fort Pierre group ; and those now before me are from 

 a locality near there on the Cheyenne, in the same geological position. 

 It is not known to occur at any other localities. 



Genus CRASSATELLINA, Meek. 



Sgnon. — Crassatellina, Meek (1871), Hayden's Second Eeport Geological Survey of the Territories, 300. 



Compare Elea, Conrad (1873), Appendix to Kerr's Geol. Eeport of North Carolina, 5 (issued 

 in advance of the report in 1873). 



Etym. — Crassatella (diiuin.). 



Type. — Crassatellina oblonga, Meek. 



Shell transversely trapezoidal, ecjuivalve, inequilateral, with free margins 

 closed and smooth within; hinge with two cardinal teeth, and one elongated 

 anterior anil one posterior lateral tooth in each valve ; anterior cardinal 

 tootli of the left valve trigonal, and deeply emarginate below; posterior very 

 much compressed, oblique, and somewhat elongated; cardinal teeth of right 

 valve diverging, with a triangular pit between for the reception of the larger 

 triangular tooth of the other valve; anterior one small, oblique, and connected 

 at its upper end with the posterior extremity of the anterior lateral ; poste- 

 rior larger, oblique, longitudinally furrowed,* and perhaps emarginated below, 

 while just behind and above it, there is a narrow oblique slit, or pit, for the 

 reception of the thin anterior cardinal of the other valve; lateral teeth 

 elongated parallel to the cardinal margins; the anterior one of the right valve, 

 and the posterior of the left, apparently continued so as to connect with the 

 upper ends of the cardinal teeth ; ligament external ; pallial line simple. 



The typical species of this genus has the general external appearance of 

 a Crassatella, from which genus, however, it is clearly removed by its hinge- 

 characters, though evidently belonging to the same family. Its muscular 

 impressions arc faintly defined, as is also the case with the pallial line, which 

 latter, however, can be followed so far back as to leave little <>r no doubt 



* The furrow of this tooth is too strongly defined in tig. :'., </. of plate 2. 



