14 



The form of the shell recalls that of many of the small species from the West 

 Indies and South America. It is found in considerable abundance. 



The Cyclas detruncata does not differ sufficiently from the type to con- 

 stitute even a variety. The Cyclas g r a c i 1 i s is a large variety of Sph. trans- 

 v e r s u m, it is a little more inflated and of a darker color. The Cyclas c o n- 

 s t r i c t a is nothing more than a difformed specimen of Say's species, having a 

 perpendicular furrow up the centre of each valve, caused by some accident 

 occurring to the shell during its growth. 



23. Sph. B a hi ens e, Spix. 



Cyclas Bahiensis, Spix, Tert. Braz. 32, pi. xxv. f. 5, 6, 1827. 



C. maculata, Anton, (non Morelet,) Wiegm. Archiv, 284, 1837. 



Pisum maculatum, Desh., Brit. Mus. Cat. 283, 1854. 



P. Bahiense " loc. sub. cit. 284, 1854. 



Musculium Bahiense, Adams, rec. gen. ii. 451, 1858. 



M. maculatum, " loc. sub. cit. ii. 451, 1858. 



Animal not observed. Shell very small, rounded-oval, inflated, inequi- 

 lateral; anterior margin narrow, curved ; posterior margin broad, subtruncate ; 

 inferior margin curved ; beaks inclined towards the anterior, large, prominent, 

 calyculate ; valves slight, interior dark yellow, irregularly mottled with dark 

 reddish spots ; lines of growth very fine ; epidermis yellowish brown, with 

 irregular spots of dark purple ; hinge margin very narrow, nearly straight ; 

 cardinal teeth small; lateral teeth comparatively strong, the posterior one 

 much the longer. 



Long. 5-32; lat. 2-16; diam. 3-32 inches. 



Hab. S. America, at Bahia in Brazil. (Cabinets Jay, Prime and others. ) 

 This, the smallest species of Sphaerium, has the peculiar appearance cha- 

 racteristic of the West Indian and South American shells of this genus. It 

 does not seem to be uncommon. Some authors, led away by its diminutive 

 size, have committed the error, as may be seen by the above synonymy, of 

 placing it under the head of Pisidium. I have never seen the Cyclas m a c u- 

 lata of Anton, (non Morelet,) but have every reason to believe, from the 

 description given of it, that it does not differ materially from this species. In 

 outline it is somewhat similar to the Sph. Barbadense; it is, however, 

 much smaller, less inflated, and the beaks are much more raised. Compared 

 to the Sph. meridionale, Nobis, and Sph. maculatum, Morelet, it is 

 smaller, more inflated, and the margins are more rounded. 



24. Sph. Barbadense, Prime, Proc. Acad. Nat. Sci. Phila., 1861. 

 Animal not observed. Shell small, rounded-oval, ventricose, subequi- 



lateral, delicate; anterior side a little the shorter and narrower; margins 

 generally rounded ; beaks slightly inclined towards the anterior, nearly cen- 

 tral, small, calyculate, approximate at apex, at times eroded; strife coarse for 

 the size of the shell, though not very distinct ; epidermis dark greenish- brown ; 

 valves slight, very convex ; cardinal teeth very small ; lateral teeth strong, 

 very much drawn up and shorter than they usually are in other species. 



Long. \ ; lat. 1-5 ; diam. 5-32 inches. 



Hab. Barbadoes, West Indies. (Cabinet Prime.) 



I have but one specimen of this species, which seems to be closely allied to 

 the bph. Bahiense of Brazil ; it is. however, much larger, more globose, 

 and its beaks are not as much raised. 



25. Sph^. mod iol if or me, Anton. 



Cyclas modioliformls, Anton, Wiegm. Archiv, 284, 1837. 



Pisidium diaphanum, Hald., Proc. Acad. Nat. Sci. Phila., i. 53, 1841. 



Pisum modioliforme, Deshayes, Brit. Mus. Cat. 283, 1854. 



Pisidium Moquinianum, Bourgt., Amen. i. 61. pi. 3, f. 1317, 1855. 



Cyclas Moquiniana, Gassies, Pisid. S. 0. f. 9, 1855. 



C. slriatella, Ferussac, Museum of Paris 



C. littoralis Collect. Michaud. 



C. Venezuelensis, Prime, Museum at Leyden. 



Musculium modioliforme, Adams, rec. gen. ii. 451, 1858. 



