BRACHIOPODA. 209 



In the fry of Pnenmodermon the end of the body is eucircled with ciliated 

 bands. (Muller.) 



Distr. 4 sp. Atlantic, India, Pacific Ocean. 



Sub-gemis ? Spongiobrancheea, D'Orbigny. S. Australis, PI. XIV. fig. 47. 

 Gill (?) forming a spongy ring at the end of the body; tentacles each with 

 6 rather large suckers. Distr. 2 sp. S. Atlantic (Fry oi Pnenmodermon ?). 

 Trichocydus, Eschscholtz, T. Dumerilii, PL XIV. fig. 48. Animal without 

 acetabuliferous tentacles ? mouth proboscidiforni; front of the head surrounded 

 with a circle of cilia, and two others round the body. 



? Pelagia, Quoy and Gaimard. 



Efyyn. Pelagns, the deep sea : (not = Pelagia, Peron and Les.) 



Type, P. alba, PI. XIV. fig. 49. Amboina. 



Animal fusiform, truncated in front, rough ; neck slightly contracted ; 

 fins small, fan-shaped. 



Cymodocea, D'Orbigny. 



Etym. Kumodoke, a Nereid. I'ype, C. diaphana, PI. XPV. fig. 50. 



Animal fusiform, truncated in front, pointed behind ; neck slightly con- 

 tracted ; fins 2 on each side, first pair large and rounded, lower pair ligulate ; 

 foot elongated ; mouth proboscidiform. Bistr. I sp. Atlantic. 



CLASS IV. BRACHIOPODA, Cuvier, 1805, 

 (= Order Pallio-brancJiiata, Blainville, Prodr. 1814.) 



The Brachiopoda are bivalve sheU-fish which diflPer from the ordinary 

 mussels, cockles, &c. in being always equal-sided, and never quite eqidvalve. 

 Their forms are symmetrical, and so commonly resemble antique lamps, 

 that they w^ere called lampades, or " lamp-shells," by the old naturalists 

 (Meuschen, 1787, Humphreys, 1797); the hole which in a lamp admits 

 the wick, serves in the lampshell for the passage of the pedicle by which 

 it is attached to submarine objects.* 



The valves of the Brachiopoda are respectively dorsal and ventral ; the 

 ventral valve is usually largest, and has a prominent beak, by which it is 

 attached, or through which the organ of adhesion passes. The dorsal, or 

 smaller valve, is always free and imperforate. The valves are articulated by 

 two cm*ved teeth, developed from the margin of the ventral valve, and re- 

 ceived by sockets in the other ; this hinge is so complete that the valves 

 cannot be separated without injury.f A few, abnormal genera, have no 



* The principal modifications of externalform presented by these shells, are given 

 in plate ] 5 ; the internal structure of each genus is illustrated in the woodcuts, which 

 are the same with those in Mr. Davidson's Introduction, and in the British Museum 

 Catalogue, They are from original studies by the author, unless otherwise stated. 



t The largest recent Terebratula cannot be opened more than ^ of an inch, except 

 by applying force. 



L 2 



