Aroa o eoi dent alls PhilipiDx, Dall ?c Simpson, 1901, Bull. U. S. 

 Gor.an., vol. "0, pt. 1, pp. 459-460. 



De so ri rt ion . 4 "A. testa elongato-obloma, suTDcuandrangiila; 

 latere antioo breviusiJloo, ang-alo fere rec'-o terrainato; postice 

 emar?:-inato ; carina obt-sa ab apice deo^irrent ei ; costis regxilaribxis, 

 prominentibus, interstitia longitudinal iter striata subaequanti- 

 bus ; ^rae'ianis parum minorib s; area dorsali me^'^iocri; li?<amento 

 illam masima ex part 0G?upante. lonp;. 22",' alt. 10"', crass. 11"'" 

 (Philippi, 184 7) 



The specimens at hand are lar?-e, t ransverselj; elongate, vpry 

 ineqnllatf-ral, decidedly convex anteriorly, higher and compressed 

 posteriorly; dorsal ir.ar"-in s trai ght, equaling the maximum length 

 of the shell; antero-lateral margin v;ith w\ obli -nr. i-»osteriorly 

 directel slope; anterior portion of the ventral margin emarginater' 

 by a long, narrow byssal gaioe, posterior portion convex; postero- 

 lateral marsrin insinuated medially, the portion dorsal to the in- 

 sinuation more produced; umbones situated at about the anterior 

 fourth of the length, bro&d, inflate"", sli^^htly prosogyrate, with 

 a slight median sulcus, the suIgtlS broadci.x,^: tov7ard the ventral 

 margin and forming a wide, shallow depression, the limits of which 

 on the ventral margin coincide with the limits of the byssal gape; 

 posterior l-eel broad, but w ell-marked ; external surface covered 

 with r?.dial ribs of uneaual size and sculpturing indifferent 



