10 



AMERICAN JOURNAL 



While this shell is entirely different in shape from the pre- 

 cedino;, it agrees with it in the general style of ornament. Both 

 have flattened whorls, truncated above and angulated below, and 

 both have heavy tubercles on the upper, and fainter ones on the 

 lower angle. Thej can be at once distinguished, however, even 

 as internal casts, by their marked dissimilarity of outline. The 

 present shell is slender, and the spire is unusually elevated ; the 

 apical angle being about 37°, while the other has an angle of 

 about 70° to 80°. In the present species I can detect no trace 

 of revolving lines, though the surface of the specimen is in a 

 nearly perfect condition, showing minute lines of growth dis- 

 tinctly. 



PHOLADOMYA. Sby. 



P. MULTILINEATA, Gabb. — PI. 5, fig. 6. 



Shell long, gibbous, beaks very prominent and placed about a 

 fourth of the length from the anterior end, which' is prominently 

 rounded in the middle ; base deep, nearly semicircular ; posterior 

 end produced in the middle, retreating above and below ; cardinal 

 margin nearly straight, posterior to the umbonal slope. Surface 

 marked by about thirty small, irregular, radiating ribs, less dis- 

 tinct at the two ends. 



Length 2-4 in., width 1-9 in., diameter 1"1 in. 



Found at the same locality as the preceding by Dr. A. 

 Blatchley. 



This species is not unlike P. ehngata, Mlinst., of the Neoco- 

 mien, but is deeper from beak to base, is shorter and has more 

 numerous ribs, though of the same general character. 



P. Nevadana, Gabb.— pi. 5, fig. 7. 



Shell small, very convex ; beaks anterior, strongly incurved, 

 umbones broadly rounded ; anterior end sloping outwards, nearly 

 straight above, convex in the middle, retreating below ; base 

 nearly straight posteriorly, most prominent directl}'' under the 

 beaks and curving upwards rapidly in advance ; posterior end 

 pretty regularly rounded ; cardinal margin nearly straight. Sur- 

 face ornamented by eight or ten small, but distinctly marked, 

 radiating ribs, most prominent on the middle, fainter posteriorly, 

 and entirely wanting on the anterior one-fourth ; these are 

 crossed by irregular lines of growth, covering the whole surface. 



Length 1-8 in., width 1*3 in., diameter of both valves 1-2 in. 

 Locality — Volcano, Nevada. Mr. J. E. Clayton. 

 Most nearly allied to P. Haicsmamii, Goldf., of the German 

 Lias, but is smaller, has more ribs, and is narrower posteriorly. 



