l'KKXA ORIENTALIS. 59 



Of eight lots in the Museum collections, from the Lias and Oxford Clay of 

 Europe, and bearing the names given in the synonymy above, all are pyritif- 

 erous, as are our Lebanon specimens; and from the coincidence of the latter 

 with the European specimens in their peculiar mineralization, condition of 

 surface, and even color, all might be supposed to have come from one and 

 the same deposit. All alike seem to have lost from the test a thin outer 

 layer, portions of which are retained on a single specimen from Salins. 

 Coll. Bird. 



Local//// and Position. — Unmistakably Jurassic, and probably from the 

 Ornati Clay of Mejdel esh Shems. 



Perna orientalis, sp. nov. 



Plate VI, figs. 1 a, b, c. 



Testa cuneato-subguadrata, subosquivalvis, aUitudo longitudinem mutto superans, 

 antice crassa, postice coarlata et in alam brevem producta : margo cardinalis obliquus, 

 rectiusculus ; area cardinalis interna tain, canaliculis parallelis ligamentum multipar- 

 titum excipientibus eircUer novem incavata ; eanaliculi spatiis interj'ectis latiores: urn- 

 bones termitiales, acicti, adunci, approximati: margo milieus insinuates ; sinus byssi 

 latus, profundus, rugosus : superficies lateralis valvarum lamellis incremenli tenuis- 

 simis inducia : impressio muscularis subcentralis valde excavata. 



Shell cuneately subquadrate, subequivalve, height greatly exceeding the 

 length, anteriorly thick, behind compressed ami produced into a short imper- 

 fect wing: hinge margin oblique, nearly straight; internal hinge area broad, 

 grooved with about nine parallel furrows, constituting a series, which receive 

 the many-parted ligament ; the furrows wider than the intervening spaces: 

 umbones terminal, sharp and hooked : anterior margin sinuated ; byssal sinus 

 broad, deep, rugose : sides of the valves overlaid with very thin lamellae of 

 growth: muscular impression nearly central and remarkably deep. 



Two specimens : one nearly entire, the other a single left valve. Dimen- 

 sions of entire shell: length, 32 mm.; height, 53 mm.; thickness, 32 mm. 

 Dimensions of single; valve: length. 35 mm.; height, 62 mm. (originally 

 about GO mm.); thickness. 23 mm. 



This species is proportionally much thicker in front, and has a relatively 

 wider and deeper byssal sinus than any hitherto described. As seen from 

 the side, its outline somewhat resembles P. iiiijlili>i<lcs Lam., which, however, 

 in all specimens and figures known to me, is comparatively Hat and thin, and 



