no AXEL A. OLSSON 



Cardinal area as in Glycymeris is generally low, triangular but with the 

 ligament restricted to a small, central pit under the beak of triangular shape. 

 Surface sculpture is varied, sometimes smooth or with concentric markings 

 only, or with radial costae and threads in different strength, the whole 

 covered by a brown-colored periostracum generally tufted. Hinge as in 

 the Glycymeridae consists of a series of obliquely set taxodont teeth on 

 both sides of the beak usually in a curved or arched form. 



Genus LIMOPSIS Sacco, 1827 



Type species by monotypy. Area aurita Brocchi. Miocene and Pliocene 

 of Italy. 



With the general characters of the family. 



The genus Limopsis has been divided into several smaller groups on 

 basis of sculpture and whether the ventral margins are smooth or cren- 

 ulated, characters poorly expressed in some species, intergradational in 

 others. Most species of Limopsis live in deep water or in cold, northern seas. 



Limopsis zonalis Dall Plate 1, figure 8 



Limopsis zonalis Dall, 1908, Bull. Mus. Comp. Zool., vol. 43, No. 6, pp. 393, 394, pi. 7, 

 figs. 6, 9. 



Shell relatively large for the genus, obliquely ovate, slightly convex 

 or compressed, white or cream-colored under a brown, villous periostracum, 

 the tufts of long hair arranged in neat radial rows. 



Height 25 mm., length 27 mm., diameter 10 mm. 



Gulf of Panama in deep water. 



This is a deep-water shell dredged by the steamer Albatross at depths 

 ranging from 555 to 782 fathoms in the Gulf of Panama. It has been in- 

 cluded here for the sake of completeness and in the expectation, that since 

 it is a fairly common species in the proper depth environment, it may yet 

 be obtained by shrimp and fish trawlers operating off the coast of Panama. 

 This species or an allied form is common as fossil in the upper Miocene of 

 northern Ecuador. 



Range — Panama. Panama: Gulf of Panama. USNM. 



Order DYSODONTIDA (Anisomyarla) 



Superfamily MTTILACEA 



Family MTTILIDAE 



Shell elongately ovate, bullet to wedge-shaped, often with an oblique 

 axis, the valves equal. Beaks small, prosogyrate, placed usually near the 

 anterior end, the umbonal slope posteriorly, often prominent and vaulted. 

 Hinge line posterior of the beaks usually straight, plain or with a crenulated 

 margin in harmony with a ribbed external sculpture, edentulous, or with 

 small dysodont teeth on the anterior lunular margin below the beaks. 

 Ligament subinternal, attached to an elongated calcified resilifer, usually- 

 white in color, compact or with a pitted or cellular basal foundation. Typi- 

 cally bimyarian, the anterior adductor scar is always much smaller than 



