G N A T II D N. 



Gcnns (;XATIIODON, Gva)j. 



Tcfla livalrifi, mjiiiralvin, trijona vel siditriijona, 

 cpidei-mide iiiduta; umboiies distanti ; di'nfiS 

 vidrce der/rce cardinales duo, parri, laterales duo, 

 po.tticus ehmgntun, anticiis cuwiformis ; valvce 

 siiii.^trce carilinalis wui.% kitendis duo, pnnllrus 

 elomjatus, anticuif cuneiformis ; I'mpressiones i/ni^ni- 

 lares duce, Interales ; ligamentum infoveam tri<j<iii(im 

 internam dispnsitum. 



Shell bivalve, sequivalve, tri^'onal or subtriL'-imal, 

 covered with ;in epidoniiis ; uniboncs distant; 

 tcelh in the right valve, two cardinal, small, two 

 lateral, posterior elongated, anterior cuneit'orni ; 

 of the left valve one cardinal, two lateral, posterior 

 elongated, anterior cnneiform ; muscular impres- 

 sions two, lateral ; ligament placed in a trigonal 

 internal pit. 



Syn. l\.\NGi.\. Desmoulins. 



This genus belongs to the Macira group, and is re- 

 markable for the cinieiform character of the anterior 

 lateral teeth, and for the deep central pit in the hinge 

 for the reception of the cartilage or ligament. None 

 of the species belong decidedly either to salt or fresh 

 water, but the type is from Lake Pontchartrain in 

 New Orleans, wliere it has been used as an article of 

 food, and three of the other species, which have much 

 thinner shells covered with a lighter epidermis, are 

 found in mud-banks in brackish water in the Gulf of 

 Mexico. One of the remaining two is from Guada- 

 loupe. 



Species 1. (jMus. Sowerby.) 



Gnathodon cuxe.^tus. Gna. festd ovafo-sublri<jond, 

 crassd, epidermide crasso olivaceo indutd ; latere 

 antico brcvi, rotundatim tuinido ; umhonibus elevatis, 

 magnis, distantibn.i ; latere postico angiilato, aide 

 angulmn depresso, ad terminum suhrostratj. 



The cuneate Gxathodos. Shell ovate, subtrigonal, 

 thick, covered with a thick olive epidermis; 



anterior side short, roundly tumid ; umboes 

 elevated, large, distant ; posterior side angular, 

 depressed in front of the angle, somewhat beaked 

 at the end. 



GiiAY. American Journal of Science. 



liangia ci/renoides, Desmoulins. 



JLd). Lake Pontchartrain, New Orleans. 



The larger the size to which specimens grow, the 

 less oval and more rostrated they become. The smaller 

 s])ecimens, with a lighter and greener epidermis, are 

 more ovate. 



specie 



(Mv 



rit.) 



Gnatiiodon Guadaloltensis. Giia. teM tenuihsrid 

 alba, subtrliio,,.;, rpnl.niiide tend, pallida sir 

 indntd; l,(t,re puslic;, „l,li,pie hiaiiijidato, produrto, 

 subrostralii, «d ttnuinuin truiioclu, latere antico 

 aiiipli), roiundo. 



The GuADALoui'E Gn.^thouon. Shell rather thin, 

 white, subtrigonal, covered with a thin, pale 

 straw-coloured epidermis ; posterior side obliquely 

 biangular, produced, somewhat beaked, truncated 

 at the end, full, rounded at the anterior side. 



Petit. Journal de Gonchyliologie. 



JIab. Guadaloupe. 



Although different looking shells, this species and 

 the following four present all the essential characters 

 of the genus. 



Species 3. (Mus. Brit.) 



Gnathodon Cantratnei. Gna. testd tenuiiisculd, albd, 

 subtrigond, epidei-mide tenui, pallide straminea 

 indutd, injlatd ; latere postico oblique biangulato, 

 jMuld producto ; latere antice breviusculo, rotunda ; 

 margine ventrali cequaliter convexo. 



Canti'.aixe's Gnatiiodon. Shell rather thin, white, 

 subtrigonal, covered with a thin, pjale straw- 



October, 1873. 



