DE. T. DAVIDSOIS' ON EECENT BRACHIOPODA. 157 



Tlwcidea niediterraiica, O. (r. Costa, Fauna del Regno di Xajjoli, p. 19, pi. ix. figs. 1-3, 18.J2 ; David- 

 son, Ann. & Mag. Nat. Hist. 2nd scr. vol. ix. p. 374, 18r)2 ; A. Adams, The Genera of Recent MoUusca, 

 p. 581, pi. cxxxii. fig. 1, 18.")8. 



Tlu'cidiuiii ijwditcrraneum, Davidson, Brit. Foss. Bracli. vol. i. Introduction, p. 77, fig. 2'.), 18.~>3 ; 

 Woodward and Gray, Catalogue of the Brachiopoda in the British Jluseum, p. 118, 1853; S. P.Wood- 

 ward, A Manual of the MoUusca, p. .'221, fig. 128, 185G; E. Sucss, Ueber die Wohnsitze dcr Brachio- 

 poden, Sitzungsb. k. Akad. dor Wissenseh. "Wien, Bd. xxxvii. p. 21G, 1859; Laeaze-Duthiers, His- 

 toirc de la Tlu'cidic mediterrancuin, Ann. des Sciences Nat. 4' ser. Zool. vol. xv. p. 259, pis. 1-5, 18G1. 



Tenbrutula (Thec'nft'n) nicillh-rnitica, L. Reeve, Couch. Icon. pi. xi. fig. 48, 1861, and Ann. & Mag. 

 Nat. Hist. 3rd ser. vol. vii. p. 18G, 1861. 



Tlwcidea mediterranea, Verani, Zool. dcs Alpes Maritimes, Nice, 1862 ; Chinu, Manuel de Conch, 

 vol. ii. p. 212, figs. 1087-1089, 1862. 



Thi'c'idiiini iiicdikiraneinii, Davidson, Geol. Mag. vol. i. j). 11, pi. i. figs. 1-3, j)!. ii. figs. 5-10, 1864 j 

 E. Deslongehaiups, Rechcrchcssur I'orgauisationdu Manteau chcz Ics Brachioj)odcs Articuk's, p. 31, pi. iii. 

 figs. 10-12, Caen, 1861; 11. C. WeinkaufF, Die Conch, des Mittelmeercs, p. 291, 1867; Dall, Amer. 

 Journ. of Conch, vol. vi. p. 151, 1870, and Proc. Acad. Nat. Sci. Philadelphia, p. 195, 1873; Gwyn 

 .Icffrcys, Proc. Zool. Soc. 1878, p. 412, & 1881, p. 919. 



Shell small, somewhat pyriformly ovate, variable in sliape, tliiciv, attached to laavinc 

 ohjects by a portion of the beak of the ventral valve. Colour dead white. Dorsal valve 

 thin, semicircular, sliglitly truncated in front ; hinge-line straight, shorter than the 

 breadth of the shell, gently convex, most so at the umbo, flattened near the margin. 

 Ventral valve more or less regularly pyriform, very convex, thickened, longitudinally 

 depressed along the middle ; beak callous, much produced, irregular on account of the 

 position and extent of its attached surf;xce ; area large, triangular. Hat, Avith a slightly 

 raised, flattened, triangular pseudo-deltidium ; no foramen ; shell-structure punctate. 

 Surface of valves smooth, marked with concentric lines of growth. In the interior of the 

 dorsal valve the hinge-plate is large, squarely oblong, prominent, and concave. There 

 exists outside each of the socket- depressions an oval muscular scar, attributed by Lacaze- 

 Duthiers to his " lateral adductor muscles " (adjustors of Hancock). A broad, thickened, 

 sloping, granulated margin encircles the valve, and forms a bridge (Plate XXIII. fig. 10, 

 h) over the small deep visceral cavity, and close to the basis of the hinge-plate, or cardinal 

 process. The granulations are larger and most prominent as they recede from the outer 

 margin. This inner denticulated or granvilated margin follows in a parallel manner the 

 margin of the shell from the In-idge-shaped process {h) until it nearly reaches the middle 

 of the frontal [c), where it suddenly stops and becomes inflected upwards. At the point 

 (c) the margin is again directed upwards, producing a second parallel curve, when at {e) 

 by another downward curve it forms a tliird short parallel concave curve, until it reaches 

 the point {f) near the centre of the valve, where it combines with the similar inflections 

 of the other lialf of tlie shell, so as to produce on tlie median line an upwardly produced 

 tongue-shaped process (/y), the angular extremity of which is directed towards the middle 

 of the bridge-shaped process {h). These four symmetrically bent ridges or lobes con- 

 stitute M. E. Dcslongchamps's " ascending apparatus," the central portions (/ and g) 

 are more elevated than the other parts, and overlie a portion of the visceral cavity. 

 The parallel grooves or spaces left between the ridges above described are partially 



21* 



