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TERTIARY FAUNA OF FLORIDA 497 



Libitina Schumacher, Essai, p. 168, 1817, type Chama oblonga Linne; Fischer, Man., p. 



1074, 1887. 

 Cypricardia Lamarck, An. s. Vert., vi., pt. i., p. 27, 1819; ed. Deshayes, vi., p. 437, 1835; 



Blainville, Man. Mai., p. 541, 1825. 

 Trapezium (Megerle) Gray, P. Z. S., 1847, P- *94- 



The genus Trapezium was proposed in Humphrey's anonymous sale cata- 

 logue for a heterogeneous group which was called the " square cockles" and 

 which included Chama oblonga Linne. Megerle restricted the genus and 

 divided it into two sections, the first typified by Chama oblonga, or guinaica, 

 and C. angulata Lam., the second including a form which had already been 

 named Gastrochana by Spengler (1783). Schumacher's Libitina and Cypri- 

 cardia Lamarck were both typified by the species which had been cited by 

 Megerle, and which is most commonly known by Lamarck's name of Cypri- 

 cardia guinaica. This was Schumacher's only species and Lamarck's first 

 species, and was taken to illustrate Cypricardia by Bowdich in 1822 and Blain- 

 ville in 1825. There can be no question as to Megerle's right to select a type 

 from Humphrey's list to bear the generic name, and also that of the forms 

 specified by Megerle, only the Chama oblonga is found in Humphrey's list. 

 Therefore the right of Trapezium to adoption stands on a solid foundation. 



Trapezium has short, papillose siphons and an entire pallial line, a small 

 byssiferous foot, the lobes of the mantle largely united, and the adductors com- 

 posed of two groups of fibres, partially separated. The shell is trapezoidal, 

 with the inner margins smooth ; the ligament, inserted in a narrow groove, is 

 elongated and external, the beaks very near the anterior end of the shell. The 

 sculpture is chiefly concentric. There are three divergent cardinals in each 

 valve, the posterior right cardinal usually bifid, the two anterior left cardinals 

 united above. The left lateral is long and strong, received between two laminae 

 of the right valve. There are no anterior laterals. Trapezium makes its ap- 

 pearance in the Mesozoic. Well-characterized species appear in the Eocene. 



The genus Coralliophaga, which bores in coral and other limy substances, 

 is much like Lithophagus in form, radially striated, has the teeth much com- 

 pressed and slender, only two instead of three cardinals and one lateral in each 

 valve, with a faint sinuation of the pallial line. 



Oryctomya has the form of Coralliophaga, but the surface is covered with 

 very fine radial lines of minute granulations, as in Eucharis, with one slender 



lost linear posterior cardinal tooth on the nymph and anteriorly another 

 lort and pedunculate, more or less bifid, in each valve; there is an obscure 

 ;ntral projection of the hinge-plate in the left valve in front of the cardinals, 



