154 DE. T. DAVIDSON ON EECENT BEACHIOPODA. 



they are small, but exceedingly numerous, and yet so blended together that it becomes 

 at last very difficult to define their shape ; and that they appear to be a white spongeous 

 mass formed of an innumerable number of short lamellae, crossing each other in every 

 direction. In his paper " Brachiopodes des cotes oceaniques de France " (' Journal de 

 Couchyliologie,' vol. xx. p. 160, pi. vi. figs. 3-9, 1872), M. P. Fischer describes at 

 great length PlatycUa anomioides, and the characters that distinguish it from Flatijdia 

 Davidson i. He gives an enlarged sketch of the brachial appendages, Avhich he likcAvise 

 states to be extremely simple. " De chaque cote de la bouche part une portion hori- 

 zontale qui se coude eusuite et forme une premiere anse ou boucle buccale. EUe est 

 continuee de chaque c6t6 par la portion currente dirigee du crochet de la valve vers le 

 bord frontal et en rapport avec la valve inferieure ou dorsale ; cette portion currente se 

 coude, decrit un ccrcle complet (anse ou boucle laterale) et revient au-dessus de la portion 

 currente en etant en rapport avec la valve dorsale ; elle se termine enfin par une 

 sinuosite dirigee vers la bouche. C'est la le rudiment de la portion spirale, qui est 

 assez developpee chez les Megerlia et beaucoup plus marquee chez les Terebratula. 

 L'appareil brachial ressemble done a celui du Platidia anomioides ; mais la boucle 

 est moius large, par rappoi't aux boucles laterales. Les cirrhes des bras sont assez longs 

 et disposes par paires, ou plutot chaque cirrhe semble se diAdser en deux filaments egaux. 

 Ce caractere a etc represente, chez le Platidia anomioides par M. Davidson." 



Owing to the extreme shortness of the peduncle, the ventral valve is kept so close to 

 the object to which it is attached that the asperities or irregularities of the rock or shell 

 are often reproduced upon it. This peculiarity is especially observable on the smaller 

 valve of PlMi/dia anomioides. 



90. PLA.TYDIA Davidsoni, E. Deslougchamps, sp. (Plate XXI. figs. 23-27.) 



Morrisia Davidsoni, E. Deslougcliamps, Ann. & INIag. Nat. Hist. 2ud ser. vol. xvi. p. 443, pi. x. figs. 

 20 a-d, 1855 ; Seguenza, Mem. Sue. Ital. Sci. Nat. vol. i. p. 07, pi. viii. fig. 5, 18G5 ; E. Suess, Ueber die 

 Wohnsitze der Brachiopoden, Sitzungsb. k. Akad. Wisseusch. Wieu, p. 212, 1859. 



Terebratula {Morrisia) Davidsoni, L. Reeve, Coucli. Icon. pi. x. fig. 42, 1861, and Ann. & Mag. Nat. 

 Hist. 3rd ser. vol. vii. p. 181, 18G1. 



Platidia Davidsoni, Dall, Amer. Journ. of Coneli. vol. vi. p. 143, 1870, and Proc. Acad. Nat. Sci. Phila- 

 delphia, 1873, p. 192; P. Fischer, Brach. des cotes oceaniques de France, Journ. de Conch, vol. xx. 

 p. 163, pi. viii. figs. 8-9, 1872, and Etudes Couch. Slarines du Dep. de la Giroude, Soc. Linn. 

 Bordeaux, t. xxix. p. 170, 1874; Monterosato, Poche note suUa Conch. Mediterr. 1875, and Note sur les 

 esp^ces du genre Platidia, Journ. de Conch, vol. xvii. p. 300, 1879. 



Shell small, semicircular or transversely oval, often irregular in shape and unequi- 

 lateral, wider than long, subpellucid, yellowish white. Dorsal valve flat and irregular, 

 assuming the shape of the objects upon which it lies in close contiguity ; concentrically 

 striated, and perforated by rather large canals ; deeply notched at the umbo by a large, 

 wide, semicircular aperture, which constitutes almost the entire foramen. Ilinge-line 

 straight, a little shorter than the breadth of the shell. Ventral valve uniformly convex, 

 cardinal angles rounded ; beak short, slightly incurved, beak-ridges sharply defined, with 

 a very narrow area or flattened space between them and the hinge-line, in the middle a 



