452 cyrenoididjE. 



obscurum, Prime. semen, Mke. 



obtusale, Pfeiff. supinum, Schmidt. 



parasiticus, Parreys. tenebrosurn, Da Costa. 



pulcbellum, D'Orb. variabile, Prime. 



pusillum, Gmel. Veatleyi, C. B. Adams. 



pygmaeum, C. B. Adams. ventricosum, Prime. 



Recluzianum, Bourg. Virginicum, Gmel. 



roseum, Scholtz. vitreum, Bisso. 



ro tun datum, Prime. zonatum, Prime. 

 rubellum, Prime. 



Fam. CYRENOIDID^. 



Labial palps elongate, narrow. Mantle-lobes free be- 

 neath, united in front and behind ; siphons two, elongated, 

 united, contractile (not retractile) ; gills two on each side, 

 unequal, narrow, united behind. Foot sub-cylindrical, 

 elongated, club-shaped. 



Shell orbicular, ventricose, thin, covered with a hard, 

 olivaceous epidermis ; valves often eroded at the beaks. 

 Hinge with three cardinal teeth in one valve, and two in 

 the other, the central tooth of the right valve bifid ; liga- 

 ment external, elongated, prominent. Muscular impres- 

 sions long and narrow ; pallial line simple. 



Genus CYRENOIDA, Joannis. 



Shell oblong or roundish, thin, ventricose, covered with 

 a dark olive epidermis. Hinge with the cardinal teeth, 

 3 2, the front and hinder of right valve thin and laminar, 

 united above, under the beak, and inclosing the small, 

 triangular, central tooth ; the two teeth of the left valve 

 united above, under the beak, and fitting into the narrow 

 fissure between the central and two united teeth in the 



