28 EXOTIC CONCHOLOGY. 



semble a land shell, is an operculated marine mollusc and found alive in the seas of 

 Spain and Portugal. Should this statement prove correct, the Cochlycopa maculata 

 must form a genus of which it is the sole species, akin on the one hand to Stru- 

 THiOLARiA, on the other to certain Buccinums. 



Order— DITHYRA. BIVALVE SHELLS. 



Tribe-ATRACHIA. 



Family— UNIONID.aS. 



Animal fluviatile : shell solid, perlaeeous ; generally with cardinal and lateral teeth. 



Sub-Family Unionin^. One valve with two cardinal and two lateral teeth : cardinal 



teeth short : the umbones or bosses smooth, or longitudinally undulated. 

 Genus — Mysca. Shell elongated oblong ovate ; cardinal teeth compressed and crenated; 



the outer sharp, and almost parallel with the anterior margin. 

 Sub-Genus — Lymnadka. Posterior hinge margin elevated and winged ; the valves con- 

 nate, the surface smooth. 



L. ALATA. THE WINGED LYMNADIA. 



Plate Vn. 



Testa magna, ovato-trigona, transversim striata ; pube in alam maximam elevata ; valvis 



margine connatis : ligamento occultato. 

 Unio Alatus, Say Encyc. Amer. Conch, pi. 4. fig. 2. Barnes' Sillim. Journal, G. p. 260. 



no. 12. Deshayes, Enc. Met. vers. t. 2, p. 583. no. 14. Lam. Anx. sans V. 6. 



p 76. no. 28. 

 Symphonota Alata, Lea on Unio, p. 62. no. 3. 

 Unio Jlatus, Sowerby's Gen. fig. 5. Wood's Cat. Sup. Mya, fig. 3. 



The subgenus Lymnadea is so natural a one, and so deservedly separated from 

 the more typical Uniones that M. Le Seur (as quoted by Lamarc) nearly twenty 

 years ago, proposed its being severed fi-om them. The alata is one of the most 

 remarkable shells of the sub-family, not so much on account of its beauty, but as 

 holding a more isolated position than any yet noticed. That it has a strong resem- 

 blance to ANODON is indisputable, but that it has a much stronger one to the Uniones, 

 cannot be questioned. Now every one who draws the distinction between analogy 

 and affinity immediately perceives, that the first of these resemblances is purely 

 analogical, while the other as Lamarc, Say, and Barnes have correctly judged, is one 

 of absolute affinity. At present, the species stands almost alone as the representative 

 of that sub-genus which typifies the Anodons. In conformity with this analogy, we 

 find the posterior dorsal margin, remarkably elevated, dilated, and winged, (so that 

 a careless observer might place it amongst the Hyria's, from which however, the dif- 

 ference of teeth, and the latter being auriculated both posteriorly and anteriorly, 



