ACEPHALA TESTACEA. 419 



ihe shortest; the valves are somewhat open, and the tubes are sepa- 

 rate and very long, as in the TeHin<E. 



There is one found on our coast, Mya hispanica, Chemn. VI, 

 iii, 21, which lives in the ooze at the depth of several inches l). 



FAMILY V. 



INCLUSA(2). 



The mantle open at tlie anterior extremity, or near the 

 middle only, for the passage of the foot, and extended from 

 the other end into a double tube, which jprojects from the 

 shell, whose extremities are always gaping. Nearly all of 

 them live buried in sand, stones, ooze or wood. Those of the 

 genus 



Mya, Lin. 



Have but tvpo valves to their oblong shell, the hinge of which varies. 

 The double tube forms a fleshy cylinder, and the foot is compressed. 

 The different forms of the hinge have furnished Messrs Daudin, La- 

 marck, &c., with the following subdivisions(3), in the first three of 

 which the ligament is internal. 



LuTRARiA, Lam., 



The Lutrarise, like the Mactrae, have a ligament inserted into a 

 large triangular cavity of each valve, and before that cavity a small 

 tooth en chevron; but the lateral plates are wanting; the gap of the 

 valves is very wide, particularly at the posterior extremity, through 

 which passes the thick, double, fleshy, respiratory and anal tube, a 

 disposition which attaches them to this family. The foot, which 

 issues at the opposite end, is small and compressed. 



(1) Improperly called by Gmelin iWadra jjiperato. 



Add Mactr a papyracea, Chemn., VI, xxiii, 231; — Mad. complanata, Id., xxiv, 

 238; — Mya nicobarica. Id., iii, 17, 18. 



(2) M- de Blainville makes two families of this one, his Pyloridea and Adesma- 

 CEA. The last includes Pholas, Teredo, and Fistulana,- the first, all the others, 

 and even Aspergillum. There are numerous genera established in this family too 

 slightly characterized to permit us to adopt them. 



(3) N.B. Half the Myse of Gmelin neither belong to this genus, nor even to this 

 family, but to Vulsella, Unio, Mactra, &c. 



