TRANSACTIONS OF WAGNER 

 880 



TERTIARY FAUNA OF FLORIDA 



His Liitrmda truncata and Schizodesina abscissa are both referable to Cynibo- 

 pjiora and differ chiefly in form. 



Subgenus SCHIZODESMA Gray, 1837. 

 Type Mactra Spengleri Linne. 

 Scissodesnia Gray (olim), 1842 ; Mactra Morch, 1853 ; not Lam., 1799. 



The type species of this group is a very remarkable form, which, if 

 isolated, would deserve generic rank. The other species, however, smooth 

 the way to the ordinary sagittate ligament, being in every way comparable in 

 the Spisula series to Mactrella in the Mactra series. The hinge, apart from 

 the purely dynamic features due to the distance between the beaks, presents 

 an interesting illustration of the inception of teeth at points subject to per- 

 cussion. The end of the strong rib which guards the ligamentary slit in either 

 valve in one valve has developed a nascent tooth or projection, and in the 

 other an obscure socket to receive it. This appears to be unique in the 

 family. The species are confined to the African coasts. 



Genus MULINIA Gray, :S37. 

 Dall, Nautilus, viii., p. 27, 1894. Type N. typica Gray {=M. edulis King). 



Shell with the ligament and resilium both enclosed in a single pit and 

 invisible externally. Laterals subequal, moderately distant; teeth normal; 

 valves closing almost hermetically ; pallial sinus short and small ; siphons 

 short; foot narrow, pointed. (See pi. 28, figs. 4, 6-9, 14.) 



Widely distributed in estuaries of the tropics and temperate seas over 

 most of the world. The most conspicuous species are from South America. 



Genus RANGrIA Desmoulins, 1832. 

 Type A', cuncata Gray (+ cyrenoidcs Desm., 1832). 



Shell like Midinia, but with the proximal end of the anterior lateral 

 vertically hooked ; laterals curved, cross-striated, more or less unequal, the 

 posterior longer ; pallial sinus small. 



Subgenus RANGIANELLA Conrad, 1868. 



Type Mactra mcndica Gld., 1851 (+ Gnath. trigonum Petit, 1853). 



Shell small, rostrate, with the laterals short, straight, and nearly smooth ; 

 pallial sinus obsolete, teeth normal. 



All the recent species of the genus are from the warmer estuaries of 

 North America. 



