(ol'^fo.f^ 



Genus: Venus Linne. 



Syst. nat. ed. X. 17.5S p. 084, ed. XII. 1707 p. I TiS. 



Animal cordaio-oblongum vel oblongum. Pallium simplex vel in maigine tentaculatura, antice 

 inferneque apertum, postice in tracheis geminis fistulosis laevibusque, connexis apice disjiinctis, vel omnino 

 liberis prosiliens. Pes triangularis vel lanceolatus, vel linguiformis, conipressus, interclum byssifer. Labia 

 buccalia parva, triangularia , acuminata. Branchiae in utroque latere binae, magnae, inaequales, subqua- 

 drangiilares, plicatae, postice conjunctae. Testa libera rarissime perfoi-ans, regularis, clausa, interdiim 

 subhians, cordata, trigona, ovata vel ovato-transversa. Cardo dentibus tribus in ntraque valva, approxi- 

 matis , apice convergentibus vel subparallelis , nonnunquam dente laterali remotiusculo sub Innula. Im- 

 pressiones musculares duplices, subaequales, subrotundatae vel piriformes. Pallii impressio plerumque 

 postice sinuosa, aliquando simplex. Ligamentum externum, nymphis linearibus interdum incrassatis fultum. 



L Subgenus: Cytherea Lamarck. 



Ann. du Mus. 18i)0 VII. p. 132, Philos. zool. I. \^m p. :<IS, Extrait d'un Cours 1S12 p. lo7, Hist 

 nat. ISIS V. p. 559. 



Cardo valvae sinistrae dentibus quatuor, quorum tribus apice convergentibus et approximatis, 

 unico remotiusculo sub lunula; valvae dextrae dentibus tribus divaricatis et approximatis, dente laterali nullo. 



1. Sectio: Tivela Link. 



Beschreib. Nat. Samml. Rostock XI. ISO" p. 152. 



Trigona Megerle v. Mühlfeldt, Entwurf ein. neu. Syst. d. Schalthiergehiiuse ISll p. 55; Schumacher 

 Essai d'un nouv. syst. 1S17 p. 153. — Tri gonella Conrad, Transact. Ameiv^%H. Soc. new. ser. V (non Da Costa.) 

 . . , V-ri^M >v,i4rc^i , n^.Scl.ö'^A.a^, V/(, 255, /SSJ. 



Animal incognitum. 



Testa trigona , cuneiformis , plus minusve aequilaf ei'alis , rarissime oblongo-triangularis, laevigata 

 vel tenuissime transversim striata, epidermide tenui, cornea, nitente induta; umbones acuti, trianguläres, 

 prominentes, subrecte incurvati; area lunulaque superficiales, in plerisque planatae; ligamentum brave, 

 prominens, nymphis linearibus late hiantibus sustentumj pallii sinus brevis, horizontalis, semicircularis vel 

 semiovatus, linguiformisque ; impressiones musculares piriformes, fere aequales, postica vix latior; cardo 

 dentibus tribus, valde convergentibus, indivisis vel partim bipartitis, dente postico nymphae pi-oximo irre- 

 gulariter ruguloso , dente lunulari elongato, remoto, compresso, in lineam rectam usque ad primum cardi- 

 nalem producto; margo internus laevis. 



Römer, Venus, Juni 1864. \ 



