374 MOLLUSCA. ACEPHALA. Spieifer. 



71. T. hemisph<Brica.~-~H.eraisiihxTica,\, with a produced incurved beak, lon- 

 gitudinally striated ; striae very numerous.— ^'owe*-. Min. Conch, t. cccxxxvi. 

 f. 1.— In Oolite. 



72. T. r'lgida. — Orbicular, plaited ; plaits granulated, increasing in number 

 towards the margin ; lesser valve nearly flat, the other convex, with a small 

 beak. — Sower. Min. Conch, t. Dxxxvi. f. 2. — In Chalk. 



73. T. slriatula Imperfectly bilobate, compressed, longitudinally ovate 



and striated ; /ront truncated, sometimes with a sinus ; striae granulated, re- 

 peatedly forked.— Man^. GeoL Suss. 131. t. xxv. f. 7? 8, and 12. Sower. Min. 

 Couch, t. DXxxvi. f. 3, 4, 5 In Chalk. 



74. T. pisum. — Suborbicular, rather square, thick, depressed, plaited ; plaits 

 numerous, simple, sometimes granulated ; front slightly elevated, beak small, 

 incurved — Sower. Min. Conch, t. DXxxvi. f. 6, 7 — In Chalk Marl. 



75. T. rostrata.— Suborbicular, gibbose, plaited ; plaits many, rounded ; 

 beak large, produced, slightly incurved, pointed ; front slightly elevated. — 

 Soiver. Min. Conch, t. Dxxxvii, f. 1, 2 — In Chalk Marl. 



. 76. T. truncata. — Semicircular, plaited ; plaits sharp, fi'om 9 to 20, some of 

 them forked ; front elevated with from 1 to 5 plaits ; hinge-line straight, equal 

 to the width of the shell ; leSser valve nearly flat, the other subconical, with 

 a straight beak, which is flat in the front. — Saicer. Min. Conch, t. Dxxxvii. — 

 In Green Sand. 



77- T. Giblsiana Suborbicular, rather triangulai*, ventricose, with nume- 

 rous rounded, simple plaits ; front much elevated, with about 10 or 12 plaits, 



flattened ; beak small, incurved, pointed ; small valve most convex Sowei: 



Min. Conch, t. Dxxxvii. f. 4. — In Green Sand. 



78. Mantelliana. — Transversely obovate, gibbose, plaited; plaits 10, sharp, 

 front elevated with 4 to 6 plaits ; beak prominent but sn\&\\.— Sower. jNIin. 

 Conch, t. DXXxvii. f. G — In Chalk Marl. 



Besides the above extended list of extinct species (of which not a few will 

 probably be found to be varieties), there are indications of a few other species 

 in the writings of British geologists ; but too obscure to warrant their inser- 

 tion here. 



Gen. SPIRIFEK. — Hinge transverse; perforation for the 

 ligament triangular, in a longitudinal flattened space un- 

 der the beak ; tM'o spirally coiled linear appendages to 

 the liinge, nearly filling the shell. 



i. S. Gitspidatus — Apex of the perforated valve broadly tiimcated, forming 

 a flat triangular space, thebase of which is in the hinge, longitudinally rib- 

 bed with a broad mesial fuiTow ; the other valve ribbed, with a mesial ridge 

 — Anomia cusp. Mart. lAn\i. Trans, iv. 45. t. iii. — Spir. cusp. Sower. Min 

 Conch, t. cxx and t. cccclxi. f. 2. — In Carboniferous Limestone. 



2. S. trigonalis.—G'ihhose., transversely striated, with about twenty-six ra- 

 diating sulci ; hinge-lino as long as the shell is wide ; front semicircular ; 

 the three central ridges elevated; beaks incun-ed, approximating. — Ano- 



mite striata, Urc, llutli. 314. t. xv. f 1 An. trigonalis. Marl. Derb. t. xxxvi. 



f. 1 Spir. trig. Sower. Min. Conch, t. cclxv. — In CarLonifcrous Limestone. 



3. S. trianyithnis " BiO'ers from S. trU/onalis pvincipallv in the sides being 



direct or slraight, not rounded, forming acute angles with the hinge; and, 



