UPPER TEIASSIC SPECIES. 103 



MYTILID^. 



? Genus MODIOMORPHA, II. & W. 



MouioMORPHA? ovATA, Meek. 



Plate 10, figs. 1 and 1 a. 



Shell obliquely ovate, much compressed; posterior side wider than the 

 anterior, and broadly rounded in outline; anterior margin narrowly rounded 

 above and sloping backward below; base prominently rounded behind the 

 middle, rounding regularly into the posterior outline, and sloping up ante- 

 riorly from behind the middle, with some appearance of being slightly 

 gaping in advance of the middle; cardinal border shorter than the valves, 

 and passing, by more or less gradual curves, into the anterior and posterior 

 margins, ranging obliquely to the longer axis of the shell ; beaks depressed 

 nearly upon a line with the hinge-margin before and behind them, com- 

 pressed and located about one-third the length of the valves from the ante- 

 rior extremity. Surface showing only moderately distinct concentric lines, 

 with sometimes very obscure undulations of growth. (Hinge and interior 

 unknown.) 



The specimens of this shell in the collection are all right valves, and have 

 the anterior ventral margin bent inward a little, so that if the other valve 

 presented the same character the lower margin, somewhat in front of the 

 middle, must have been more or less gaping. Without seeing its hinge and 

 interior, we can only guess at its affinities. In general appearance, it 

 reminds one of some of the broad compressed species of Modiolopsis from 

 the Silurian; but it is apparently as nearly like some of the species included 

 in the new Devonian and Carboniferous genus Modiomorpha. That it really 

 belongs to either of these genera, however, is at least improbable, and the 

 chances are in favor of the conclusion that it will be found to belong to an 

 undescribed genus. If so, I would propose for it the name Modiolina. 



Locality and position. — North fork of Buena Vista Canon, West Hum- 

 boldt Range; Upper Trias. 



MoDiOMOEPHA? LATA, Meek. 

 Plate 10, 6g. 2. 



Shell transversely ovate, moderately convex in the central and um- 

 bonal regions, and compressed behind; posterior side distinctly wider than the 



