228 AXEL A. OLSSON 



amongst beach drift. The habitat station of Cyrenoida is in brackish water 

 associated with mangrove swamps. Two species have been described from 

 the Panamic region. 



1. Shell of medium size (length up to 20 mm.), beaks anterior in position. 



C. panamensis 



2. Shell smaller (length to about 7 mm.), beaks more central. 



C. insula 



Cyrenoida insula Morrison 



Cyrenoida insula Morrison, 1946, Sraitli, Misc. Coll., vol. 106, No. 6, p. 45, pi. 1, figs. 8-11. 



Shell small, lenticular, suborbicular, vitreous, blue-white, under a pale 

 corneous epidermis. Umbones smooth, Httle prominent, scarcely projecting 

 above the general outline. Sculpture of minute, crowded concentric striae. 

 Hinge well developed, lightly arcuate, wider anteriorly. Anterior and ventral 

 margins evenly rounded as one curve. Posterior margin almost evenly round- 

 ed, a trifle more abruptly rounded into the dorsal and ventral margins. 



Length 6.7 mm., height 6.2 mm., diameter 3.8 mm. 



This species was collected from pools in the mud of a small mangrove 

 swamp on the west side of San Jose Island. It was found only in small 

 numbers and did not seem to be abundant in any of the mangrove swamps 

 on the island. (Morrison, 1946.) 



Range — Panama. Panama: San Jose Island of the Pearl Island group. 



Cyrenoida panamensis Pilsbry and Zetek Plate 84, figures 3, 3a 



Cyrenoida panamensis Pilsbry and Zetek, 1931, Nautilus, vol. 45, No. 2, p. 69, pi. 3, 

 fig. 4. 



The shell is rounded, modified by the subtruncate posterior end, the 

 weak dorsal curvature and the rather prominent beaks, which turn more 

 to the anterior end than in C. americana; plump. Covered with a dull 

 chamois periostracum with some Isabella colored concentric streaks or suf- 

 fusion; this periostracum is very minutely laminate along the lines of 

 growth, and is persistent except at the beaks of old specimens. The interior 

 is grayish white. Hinge rather narrow. Anterior limb or both limbs of the 

 left cardinal teeth bifid at summit. 



Length 18 mm., height 17.5 mm., diameter 10.3 mm. Panama City, 

 Panama. (Pilsbry and Zetek, 1931.) 



According to the authors, this species was once abundant in that part 

 of Panama City now known as Hatillo, living along a narrow stretch of 

 beach, brackish, and where mangrove then grew; the area is now well 

 drained and built up; the species is probably living further east where 

 similar conditions now prevail. 



Range — Panama. Panama: Panama City. 



Superfamily EEYCDfACEA 



The species of this superfamily form a composite group composed mostly 

 of small (often minute) pelecypods known collectively as leptons. Many 

 species are parasitic or commensal on other marine invertebrates, hence 

 their shell and hinge often show characters suggestive of both immaturity 



