EI{AC1II01‘()1)A 
OF Till-: 
CRETACEOUS HOCKS OE SOUTHERN INUIA. 
S Lili-kingdom, MO LLUSC A . 
Class, ErtAClIIOPODA, Oumer. 
Character. — Acepludous 3Iullusca icith Ihe mantle divided into a dorsal and 
ventral half, each provided at the margin with hoioty or chitinous setce ; body smatt, 
symmetrical, or very nearly so ; month anterior, nearly central, at the base between 
a pair of feshy, internally sulcatcd and ciliated, more or less spirally twisted arms, 
which chiejly serve the purpose of branchice, and are often supported by solid calcareous 
processes. 
The two mantle lobes secrete a bivalved, incquivalved, generally symmetrical 
shell, the two valves being sometimes joined to each other by a pair of hinge-teeth, 
hut they are always kept together by adductor muscles, and are opened by cardinal 
muscles ; the calcareous brachial apparatus, if present, is always attached to the 
smaller, or luemal valve, while the larger or neural one is sometimes partially or 
entirely grown to other objects, and more generally provided Avith a perforated umbo, 
through which a fleshy peduncle is protruded, serving for temporary or permanent 
attachment of the animals. All species are marine. 
The history and organisation of the 13rachiop.oda — or Brachionacephala, as 
Bronn suggested to call them — have been exhaustively treated by Davidson and 
Broun in their Avorks already alluded to. I shall only refer to a fcAV of the more 
important anatomical and structm-al points, as explanatoiy of the above diagnosis. 
As regards then external covering — the shell — the ]3rachiopoda oiler several 
points of resemblance to the Belecypoda, hut they essentially diller from them in 
the arrangement of the internal organs, and in this respect are more closely allied 
to the Saccopoda, and the arm-bearing division of the Ciliopoda. 
The body is vciy small, lying at the base betAveen the tAVo almost entirely 
separated and unequal portions of the mantle, Avhich are dorso-ventrally situated 
respecting each other, Avhile in the Belecypoda the tAvo halves enclose the body later- 
ally. Each half of the mantle consists of several layers, the outer of AA'hich 
