NO. 1237. SYNOPSIS OF THE LUCINACEA— BALL. 817 



Family CYRENELLIDJ^. 



The shells of this group, with a Lucinoid animal and Diplodonta- 

 like shell, exhibit a hinge structure which is wholly distinct from any 

 other of the Lucinacea. They are of brackish or fresh water situs 

 and contined, as far as known, to the borders of the subtropical Atlan- 

 tic and the Tertiaries of the southern United States. 



Genus CYRENOIDA Joannis. 



This is Gyrerwida Joannis, June, 1835, Cyrenella Deshayes, Feb., 

 1836, and Cyrenoldes Sowerb}^, 18-12. Type, G. dupontia Joannis, 

 Senegal. 



Shell thin, inflated, suborbicular, with a brownish or ^^ellowish peri- 

 ostracum, concentrically feel)ly striated; adductor scars sul)equal, 

 elongate-ovate, the anterior projecting ver}^ little into the area within 

 the pallial line, internal margins not crenulate; hinge with a long- 

 external ligament enfolding a smaller resilium; right valve with two, 

 and left with one 1>~~ -shaped cardinal laminte, the ventral one in the 

 right valve shorter and more compressed, the *' hooks" or shorter 

 limbs of the lamina^ tending to be sulcate or bitid. There are no 

 laterals. The original type appears to have had a defective hinge, as 

 the flgure of this part of the shell given by Joannis is erroneous, 



CYRENOIDA AMERICANA Morelet, 1851. 



Cuba and Porto Kico, in the deltas of streams. 



More transverse than the African species and with a more delicate 

 hinge and less prominent um bones. ^ 



CYRENOIDA FLORIDANA Dall, 1896. 



Brunswick, Georgia, south to the Everglades of Forida, and in 

 west Florida, north to Charlotte Harbor and A'icinity, in ])raekish 

 marshes. 



Smaller and more delicate and less (puidrat(^. than the l*orto Rico 

 species. 



A much larger species occurs in the Pliocene of the Caloosahatchie 

 beds of Florida, and has been named (1896) CI caloomensis Dall. It 

 reaches a length of 31 mm. 



NOTES AND 1JP:SCRIPTI0NS OF NEW SPECIES. 



THYASIRA BISECTA (Conrad). 



(Plate XL, lig. 8; plate XLII, tig. 5.) 



Figures are of a recent specimen with a length of 50 nun., which 

 was dredged southeast of Alaska Peninsula in 69 fathoms, nuid, the 

 bottom temperature being -14^^ F. The younger specimens dredged at 



^ See Porto Rico Report, pi. vi, tig. 5. 

 Proc. N. M. vol. xxiii 52 



