CONCHIFERA. 723 



., Rhynconella FISCHER (anatomy by OWEN Zool Trans. 

 Vol. i. pt. 2). On all the genera of this division see especially 

 DAVIDSON on the classification of recent Brachiopoda, Ann. and 

 Mag. of Nat. Hist., new ser. ix. 1851, pp. 361377.] 



Much more numerous than the recent species are the fossil, amongst 

 which we cite that alone, on account of its peculiarly symmetrical form, 

 which FABIO COLONNA likened to two mussels joined together: Terebratula 

 discoidea LAM., Terebratula diphya COL., VON BUCH Encycl. meth., Vers. 

 PL 240, fig. 4, from the chalk-formation, especially found in Italy. 



Comp. L. VON BUCH Ueber Terebrateln mit einem Versuch sie zu classiji- 

 ciren und zu beschreiben, mit $lithogr. Tafeln, Berlin, 1834, 4to. (Abhandl. 

 der Alcad. der Wissensch. in Berlin, Physilc. Klasse 1833). 



Spirifer SOWERBY, Delthyris DALM., Trigonotreta KOENIG, BRONN. 

 Foramen of larger valve triangular, marginal. Supports of arms 

 rolled spirally. 



Comp. SOWERBY Linn. Transact, xn. p. 514, fig. 9; L. VON BUCH 

 Ueber Delthyris oder Spirifer und Orthis, mit 2 lithogr. Taf. Berlin, 1837. 

 4to. (Abh. der AJcad. in Berlin, Physilc. Kl. 1836). 



The shells are usually much extended in the breadth, as, Spirifer spe- 

 ciosus BRONN, Leth. geogn. Tab. n. fig. 15. 



All the species belong to the older, in great part to the transition-forma- 

 tions. In the Lias 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 SOWERBY, Strophomena RAFIN., BRONN, Leptena 

 DALM. 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. DESHAYES thinks that these conchifers were not attached, but 

 moved freely like most of the lamellibranchiates. Sp. Productus tubuliferus 

 DESH., Strephomena aculeata BRONN, Lethcea geogn. Tab. in. fig. r, &c. 

 Some writers distinguish Strophomena as a distinct genus from Producing. 

 See on this and other genera which we here omit, W. KING in Ann. and 

 Magaz. of Nat. Hist. Vol. 18, 1846, pp. 26 42 and pp. 83 94, and on 

 Productus L. VON BUCH in Abhandl. der Alcad. in Berlin, Physik. Klasse, 

 1841. The admirable Monograph of DAVIDSON, On the British Oolitic and 

 Liassic 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 Palseontographical Society of London in the years 1851, 1852, 1854, 

 and are especially referred to in this division. 



ORDER II. Lamellibranchiata. 



Body compressed, covered on both sides by a lamina of the 

 mantle. Branchiae at the sides of the body placed under each lobe 



462 



