CONCHIFERA. 723 
D’Orz., Rhynconella Fiscunr (anatomy by Owrn Zool. Trans. 
Vol. 1. pt. 2). On all the genera of this division see especially 
Davipson on the classification of recent Brachiopoda, Ann. and 
Mag. of Nat. Hist., new ser. 1x. 1851, pp. 361—377.] 
Much more numerous than the recent species are the fossil, amongst 
which we cite that alone, on account of its peculiarly symmetrical form, 
which Fazio Cotonna likened to two mussels joined together: Terebratula 
discoidea LAm., Terebratula diphya Cou., Von Bucu Encycl. méth., Vers. 
Pl. 240, fig. 4, from the chalk-formation, especially found in Italy. 
Comp. L. Von Bucu Veber Terebrateln mit einem Versuch sie zu classi fi- 
ciren und zu beschreiben, mit 3 lithogr. Tafeln, Berlin, 1834, 4to. (Abhandl. 
der Akad. der Wissensch. in Berlin, Physik. Klasse 183 3). 
Spirifer SowErsy, Delthyris Daum., Trigonotretu Koryic, Bronn. 
Foramen of larger valve triangular, marginal. Supports of arms 
rolled spirally. 
Comp. Sowrrsy Linn. Transact. x1r. p. $14, fig. 9;—L. Von Buca 
Ucher Delthyris oder Spirifer und Orthis, mit 2 lithogr. Taf. Berlin, 1837, 
4to. (Abh. der Akad. in Berlin, Physik. Kl. 1836). 
The shells are usually much extended in the breadth, as, Spirifer spe- 
ciosus BRonn, Leth. geogn. Tab. 1. fig. 15. 
All the species belong to the older, in great part to the transition-forma- 
tions. In the ZLias or lowest oolitic strata, the last species of this genus is 
found, Spirifer Walcottii, which is thus met with no more amongst the 
remains of living creatures. 
Productus SowERsy, Strophomena RAFIN., Bronn, Leptena 
Datm. Hinge linear, straight. Shell inequivalve, alate, almost 
semiorbicular, with larger valve gibbous, imperforate. 
An entirely extinct genus from the oldest periods of the history of our 
earth. DEsHayYES thinks that these conchifers were not attached, but 
moved freely like most of the lamellibranchiates, Sp. Productus tubuliferus 
DeEsu., Strephomena aculeata Bronn, Lethea geogn. Tab. 111. fig. 1, &e. 
Some writers distinguish Strophomena as a distinct genus from Productus. 
See on this and other genera which we here omit, W. Kine in Ann. and 
Magaz. of Nat. Hist. Vol. 18, 1846, pp. 26—42 and pp. 83—94, and on 
Productus L. Von Bucu in Abhandl. der Akad. in Berlin, Physik. Klasse, 
1841. The admirable Monograph of Davmmson, On the British Oolitic and 
Liassie Brachiopoda, with an introduction on the classification, and a chap- 
ter by CaRPENTER, On the intimate structure of the shells of Brachiopoda, 
besides that of Owen, already cited on the Anatomy, were published for 
the Paleontographical Society of London in the years 1851, 1852, 1854, 
and are especially referred to in this division. 
Orver II. Lamellibranchiata. 
Body compressed, covered on both sides by a lamina of the 
mantle. Branchix at the sides of the body placed under each lobe 
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