254 AXEL A. OLSSON 



Microcardinm panamensis (Dall) Plate 39, figure 4 



Protocardium panamensis Dall, 1908, Bull. Mus. Comp. Zoology, vol. 43, No. 6, p. 415, 

 pi. 18, fig. 1.— Maxwell Smith, 1944, Panamic Marine Shells, p. 58, fig. 742. 



Shell small, (the adult type 13.5 mm. long), thin and delicate, convex, 

 subovate to subquadrate, the posterior side straighter, the prominent um- 

 bones subcentral. Umbonal slope rounded. Ribs numerous, on an average 

 specimen numbering from 26 to 33 on the anterior and middle surfaces and 

 21 to 23 on the posterior; each set fading out laterally. The anterior and 

 middle set have smooth-topped or slightly noded ribs, their interspaces 

 coarsely cross-threaded so as to form deep pits; the posterior ribs are nar- 

 rower than their interspaces which are more finely cross-threaded; each 4th 

 or 5th and 9th or 10th ribs on the posterior slope bears small spinules, the 

 others are generally without. 



Length 13.5 mm., height 13.5 mm., diameter 9 mm. Gulf of Panama 

 (Dall). 



Range — Panama. Panama. Gulf of Panama in 182 fathoms (Albatross 

 Exp.). 



Microcardimn paziannm (Dall) Plate 39, figure 3 



Protocardia paziana Dall, 1916, Proc. U. S. Nat. Museum, vol. 52, No. 2183, p. 412 



off La Paz, Gulf of California, in 10 fra. 

 Cardium {Microcardium) pazianum (Dall), Hertlein and Strong, 1947, Zoologica, vol. 



31, pt. 4, p. 142, pi. 1, figs. 9, 12, 15, and 16. 



Shell small (length to about 15 mm., but usually much smaller), thin, 

 rounded, the posterior side noticeably produced and narrower, the anterior 

 side convex. Ihe anterior and middle surface have numerous, (to about 40) 

 minutely nodulous riblets, each giving the effect of a string of beads; on 

 the posterior slope the riblets number about 22, are larger and when intact, 

 each second or third interspace bears a row of large, coarse granules. 



Length 10 mm., height 8.6 mm., diameter 6 mm. Off La Paz, Gulf of 

 California. (Dall). 



Resembles M. panamensis but is usually smaller, its riblets on the 

 anterior side are more numerous and more coarsely concentrically nodulous 

 while on the posterior slope, the sculpture is more strongly spinose or 

 granulose. The species is likewise distinguished in that the posterior side 

 is noticeably narrowed and produced, its characteristic sculpture covering 

 a larger surface. 



This appears to be a commoner, more widely distributed, and a shal- 

 lower-water species than M. panamensis. Numerous records of its occurrence 

 from the Gulf of California to Panama are given by Hertlein and Strong. 



Range — Gulf of California southward to Ecuador. Northern records see 

 Hertlein and Strong. Ecuador: Esmeraldas in about 10 to 30 fathoms. 



Genus LOPHOCARDIUM Fischer, 1887 



Type species by monotypy, Cardium cwningii Broderip. 



Shell elongately ovate, longer than high, thin, convex, with full, sub- 

 median umbones. The posterior side is lower, slightly gaping at the end, the 

 posterior area separated sharply from the rest of disk by a fringe or elevated 



