35 



American Tertiary Shells 



25 



phalt Company of Philadelphia. 



Pleurophopsis unioides var. fernandensis, n. sp., PI. 3. Fig. 13, 14. 



Description. — Size and shape as indicated by the figures ; 

 umbonal ridge which extends nearly to the posterior, ventral mar- 

 gin well marked in the young ; two very wide, deep furrows ex- 

 tend on the anterior portion of the shell from the area of the beak 

 to the ventral margin ; the groove most anterior extends prac- 

 tically straight to the basal margin, while the second groove ex- 

 tends obliquely toward the posterior end of the shell ; where this 

 furrow merges into the base, the margin of the shell forms on in- 

 dentation, from here the anterior portion is drawn out at about 

 an angle of 30 degrees to the dorsal margin ; this gives the form 

 on aviculoid appearance, this extreme contortion is characteristic 

 of the large, adult specimens, the young show the two anterior 

 furrows but are more moderate in form, showing the shape of the 

 parent species, P. unioides ; surface sculpture consists of heavy 

 lines of growth which in the adult become very rugose along the 

 1 mbonal ridge ; longitude of shell 134 mm ; altitude 55 mm. 



Type and specimens figured. — Pal. Museum, Cornell Univ. 



Age. — Probably Middle Tertiary. 



Locality. — "One mile west of Godineau River on the shore of 

 the Gulf of Paria, about midway between San Fernando and La 

 Brea, Trinidad." 



Collected by A. C. Veatch in 191 2, then of the General As- 

 phalt Company of Poiladelphia. 



THYASIRA Leach 



Thyaslra adoccasa, n. sp., PI. 3. Fig, 15, 16. 



Unto sp. Maury, Jour. Acad. Nat. Sci. Phila., 2nd ser. vol. XV, 1912, 

 p. 50, pi. IX, fig. r. 



Description. — Shell attaining a very great size ; shape as in- 

 dicated by the fignres, in the young form the shape is more quad- 

 rate, the posterior end less attenuated ; in the young and inter- 

 mediate stages a very characteristic, strong fold or flexure extends 

 from the beaks to the posterior margin ; this groove which is 

 so marked in the early and medium stages is greatly reduced in 



