PANAMIC-PACIFIC PELECYPODA 53 



thus equalling in size some of the fossil forms. The surface is marked with 

 from 7 to 12 wide flat rays between deep channels which show on the 

 inside as prominent radial ribs. 



Woodring^, who has examined the types of S. johnsoni and S. agassizii, 

 questioned whether there are two species in the lot as the characters men- 

 tioned by Dall as to the number of rayed channels is variable and their 

 count a matter of personal judgement. The type of S. johnsoni is a specimen 

 taken off the coast of Lower California in 1,005 fathoms, that of S. agassizii 

 from the Gulf of Panama in 1,672 fathoms. 



Range — In deep water from Oregon to Punta Aguja, Peru, 



Subgenus I'ETllASMA Dall, 1908 



Type species by original designation, Solemya borealis Totten. 



Solemya (Petrasma) panamensis Dall 



Solemya panamensis Dall, 1908, Nautilus, vol. 22, No, 1, p, 2, 



Solemya (Petrasma) panamensis Dall, 1908, Bull. Mus. Comp. Zool., vol. 43, No. 6, p. 



366 Panama Bay in 29J^ fms. — Hertlein and Strong, 1940, Zoologica, vol. 25, 



pt. 4, pp. 377, 378. 

 Solemya panamensis Dall, Pilsbry and Lowe, 1932, Proc. Acad. Nat. Sci. Philadelphia, 



vol. 84, p. 141 on mud flats at extreme tide, rare, La Paz. 



Length of valves exclusive of periostracum 39 mm., the shell thin, 

 elongate-oval, the posterior end more pointedly and the anterior end more 

 bluntly rounded. Periostracum brown, glossy, recurved over the margins 

 of the valves, not produced into long processes, though more or less broken 

 up beyond the margins. Anterior surface of valves radiately marked with 

 eight or nine obscure rays, the middle zone with few sparse rays, the posterior 

 with six or seven, more closely spaced, followed by a smooth area behind 

 the beaks. 



This is a smaller, more expanded, and less sharply truncate anteriorly 

 than S. agassizii of the same length. Also easily separated by hinge differ- 

 ences. A shallow water species, sometimes encountered on mud flats at 

 extreme low tide. 



Range — Panama Bay northward to California. 



Or,der FALAEOTAXODONTIDA 

 Superfamily NUCULACEA 

 Family NUCULIDAE 



The shells of this family are usually small, ovate to subtrigonal, with a 

 shiny, pearly or nacreous interior, equivalve but inequilateral, the anterior 

 side being longer than the posterior. Surface smooth, often polished or 

 marked with radial or concentric threads or riblets, sometimes finely can- 

 cellate, the pattern often divaricate. Hinge plate generally heavy, curved 

 or bent in the middle with a central resilifer or chondrophoral pit bordered 

 on the sides by an anterior and posterior series of small but numerous taxo- 

 dont teeth. Ventral margin of valves smooth or crenulate. 



Mostly small shells, often known as "Nut Shells". They are widely 

 distributed in all seas, occurring most plentifully on a mud bottom. 

 ^Woodring, W. P., 1938, Prof. Paper 190, U. S. Geol. Sur., p. 27. 



