SIMPSONKLLA 1069 



Unio velaris Sowerby, Conch. Icon., XVI, 1868, pi. lxxii, fig. 



368. 

 Physunio velaris Simpson, Syn., 1900, p. 831. — Haas, Conch. 



Cab., Unio, 1912, pi. 34, fig. 9. 



I have never seen this species and as I know nothing regard- 

 ing its beak sculpture I cannot be certain whether it belongs 

 here or in Hyriopsis. Sowerby does not say anything about 

 its nacre. Compared with P. eximius, to which it seems most 

 closely related, it is a shorter shell, more rounded behind and 

 lighter colored. I think it likely that the shell figured is young. 



Genus SIMPSONELLA Cockerell, 1903. 



DallicUa Simpson, Syn., 1900, p. 832; non Cossman, 1895. 

 Siinpsonella Cockereu,, Naut., XVI, 1903, p. 118. 



Shell subtrapezoidal, generally thin, inflated, with a low, 

 rounded posterior ridge and rather full beaks, which have 

 somewhat zigzag-radial sculpture, with a row of chevron- 

 shaped folds running some distance down the posterior ridge, 

 and with fine corrugations in front of the beaks ; epidermis 

 somewhat cloth-like; substance of the shell of a peculiar pur- 

 plish-brown tint ; hinge line narrow ; teeth imperfectly de- 

 veloped, sometimes reduced to mere rudiments, when present 

 consisting of greatly compressed, feeble pseudocardinals and 

 laterals ; beak cavities rather shallow ; dorsal scars one to a 

 few, scattered ; muscle scars faint ; prismatic border wide. 



Animal unknown. 



So far as conchological characters go, and we know nothing 

 of the anatomy of the above group, it would seem that Simp- 

 sonella was closely related to Pseudodon. In the present 

 genus pseudocardinals and laterals are generally present, 

 though quite commonly in greatly reduced form, they are 

 compressed or lamellar, while in Pseudodon the laterals are 

 wanting and the pseudocardinals are smooth and usually more 

 or less tubercular. There is a peculiar purplish or coppery 

 tint present in all the members of this genus. The group of 

 S. insularis seems to partially connect it with Pseudodon. 



Type, Anodonta purpurea Valenciennes. 



