DE. T. DAVIDSON ON EECENT BRACHIOPODA. 129 



Ortltis detruncaia, G. Michelotti, Descr. des Foss. Jliocenes, p. 78, 181"; A. Aradas, Descr. delle 

 Conch. Foss. di Gravitelli, p. 14, 18-17. 



Terebratula pectiniformis, Costa, Mem. Reale Accad. delle Scienze di Nap. vol. v. p. 39, pi. i. fig. G. 



Orthis di'lrancata, Costa, Fauua del Regno di Napoli, pi. ii. figs. 6-7, 18."j1. 



Aryiope dccollata, Davidson, Ann. & Mag. Nat. Hist. vol. ix. p. 373, 1852; "Woodward & (Jniy, Cat. 

 of the Brachiopoda in the Brit. Mus. p. 113, 1853; Davidson, Brit. Foss. Bracli. vol. i. Introduction, 

 p. 73, figs. 22-23, and pi. vi. figs. 32-33, 1853 ; S. P. Woodward, A Manual of the Mollusca, p. 220, 1856. 



Jrt/iojje detrmicata and A. dccollata, Pictet, Traite do Pal. vol. iv. p. 27, 1857. 



Aryiope decollala, A. Adams, The Genera of Recent Mollusca, vol. ii. pi. exxxi. fig. 6, 1858; Deslong- 

 champs. Bull. Soc. Linn, de Normandie, vol. iii. p. 122, 1858. 



Orihis decoUata, Requiem, Coq. de la Corse, p. 35. 



Artjiope decoUata, Gwyu Jeffreys, Ann. & Mag. Nat. Hist. 3rd ser. vol. ii. p. 124, 1858; E. Suess, 

 Ueber die Wohnsitzc der Brach. Acad, der Wissenscli. Wien, Bd. xxxvii. p. 213, 1859. 



Terebratula {Arglope) decollata, Lovell Reeve, Conch. Icon., Monogr. of Ter. pi. x. fig. 43, 18G1 ; and 

 Ann. & Mag. Nat. Hist. 3rd ser. vol. vii. p. 185, 1801. 



Argiope decollata, Chemnitz, Man. de Conch, ii. p. 209, figs. 1067-1069, 1862; E. Deslongchamps, 

 Recherchcs sur I'Organisation du Manteau chez les Brachiopodes, p. 291, pi. iii. figs. 8, 9, 1864- 

 Gwyn Jefi"reys, Brit. Conch, vol. ii. p. 18, 1863, and vol. v. p. 164, pi. xix. fig. 3, 1869; Davidson, 

 Brachiopoda of the jMaltese Islands, Ann. & Mag. Nat. Hist. 3rd ser. vol. xiv. p. 9, pi. i. figs. 11, 12, 

 1864; Seguenza, Mem. Soe. Ital. di Scienze Nat. vol. i. p. 69, 1865 ; S. Brusina, Moll. Dalmati, p. 47, 

 1866 ; C. WeinkaufF, Die Conch, des Mittelmeeres, p. 288, 1867 ; Davidson, Ital. Tert. Brach., Gcol. 

 Mag. vol. vii. pi. xxi. figs. 5-8, 1870. 



Megathyris decollata, Dall, Amer. Journ. of Conch, vol. vi. p. 145, 1870, and Proc. Acad. Nat. Sci. 

 Philadelphia, 1873, p. 193. 



xirgiope decollata, P. Fischer, Brachiopodes des Cotes Oceaniques de France, Journ. de Conch, vol. viii. 

 p. 377, 1870, and Conchyl. dc la Gironde, Soc. Linn, de Bordeaux, p. 172, 1874; Gwyn Jeffreys, Proc. 

 Zool. Soc. 1878, p. 409; Zittel, Handbueh der Palaontologie, p. 697, 1880; Davidson, Report on 

 the Brachiopoda, Voyage of H.M.S. ' Challenger,' Zool. i. p. 57, pi. iv. figs. 12, 13, 1880. 



Megathyrh decollata, J. de IMorgan, Bull. Soc. G(iol. de France, vol. viii. 1883. 



Argiope decollata, Schulgin, Zeitschrift fiir wissensch. Zool. Band xli. pi. viii. figs. 1-11, 1884. 



Shell small, variable in shape, generally semioval or obscurely subpentagonal, rounded, 

 laterally and in front, obtusely angular posteriorly. Hinge-line nearly straight, as long 

 as the greatest breadth of the shell, with generally acute cardinal extremities. Dorsal 

 valve semicircular, gently convex. Ventral valve rather deeper than the opposite one ; 

 beak prominent, nearly straight ; foramen large, incomplete, margined anteriorly by a 

 considerable portion of the umbo, laterally by very small rudimentary deltidial plates ; 

 beak-ridges sharply defined, leaving between them and the hiuge-line a wide triangular, 

 flattened area. Surface of valves ornamented with from ten to fourteen rounded cori-e- 

 sponding ribs, the two central ones generally deviating so as to admit one or two shorter 

 ribs between them. Surface of both valves crossed by equidistant, slightly projecting 

 lines. Teeth short, sockets broad and deep. In the interior of the dorsal vahe the 

 hinge-plate is long, narrow, and concave, without any defined or prominent cardinal 

 process. Three or five submarginal septa, most elevated anteriorly ; the three central 

 ones the largest and most prominent. The loop, composed of a ril^and-shaped lamella, 

 is first attached to the hinge-plate, then cvu'ved to fit into the hollows between the 



