56 THE VOYAGE OF H.M.S. CHALLENGEE. 



circular foramen. Ventral valve convex, of moderate depth, liinge-line straight, area 

 small. Beak very slightly incurved, foramen situated under its angular extremity, 

 margined by narrow deltidial plates. Surface smooth, marked with concentric lines of 

 growth. In the interior of the dorsal valve the loop is small, and not reflected ; hut 

 the converging principal branches are first attached to liinge, and again to the upper 

 extremity of a small vertical medium septum. Peduncle very short ; animal possessed 

 of sigmoid labial appendages. Length 4, breadth 5, depth 2 mm. 



Habitat. — Two examples were dredged by the Challenger Expedition, attached to two 



examples of Waldheiniia kerguelenensis, ofi" Marion Island, on December 26, 1873, in 100 



fathoms. Five likewise off Prince Edward's Island, close to Marion Island, on December 



26, 1873. It was also dredged in the Mediterranean by Professor E. Forbes at a depth of 



91 fathoms, and by Mr W. S. Kent off the Portugal coast, near the mouth of the Tagus. 



Platydia anomioides occurs fossil in the Pliocene deposits of SicUy. 



Observations. — The animal of this interesting and well-marked genus has not yet been 



sufliciently anatomically studied. The arrangements of the labial appendages are very 



remarkable. They were briefly described and figured by Signor Costa in 1843, and 



by myself in 1852, but more particularly in 1864 by Mr E. Deslongchamps, in his 



valuable memoir, Recherches sur I'Organisation du Manteau chez les Brachiopodes 



articules. His observations were, however, like my own, unfortunately founded on 



dried specimens. He states that the brachial appendages are much more simple than in 



other genera of the Brachiopoda, and that the two principal branches which lie close 



to each other at their origin, and towards the centre of the shell, deviate by a curve, and 



having made almost a complete circle, return close to their origin, without forming a spiral. 



But his most important observations relate to the mantle which he states to be so thickly 



coated with spicules that it is impossible to separate it from the brachial appendages 



without injuring them ; that they are small, but exceedingly numerous, and get so 



blended together that it becomes at last very difiicult to define their shape ; that they 



appear to be a white spongeous mass formed of an innumerable number of short lamella 



crossing each other in every direction. In his paper Sur les Brachiopodes des Cotes 



Oceaniques de la France (Journal de Conchyliologie, 3d series, vol. xii. p. 160, pi. vi. 



figs. 3-9, 1872), Mr P. Fischer describes at great length Platydia anomioides and the 



characters that distinguish it from Platydia davidsoni. He gives an enlarged sketch 



of the brachial appendages which he likewise states to be extremely simple. " De 



chaque cote de la bouche part une portion horizontale qui se coude ensuite et forme 



une premiere anse ou boucle buccale. EUe est continuee de chaque cote par la portion 



currante dirigee du crochet de la valve vers le bord frontal et en rapport avec la valve 



inferieiTre ou dorsale : cette portion currante se sonde, deerit un circle complet et revient 



au-dessus de la portion currente en etant en rapport avec la valve dorsale : elle se termine 



enfin par une sinuosity dirigee vers la bouche. C'est la le rudiment de la portion sjDirale, 



