650 



BRACIIIOPODA. 



loads to a sUgUUy-coiled intestine, wliicli may have an anus (Teeienteeata), 

 or may not (Clisieniekata). 



J^ij. 5: — A NoN-HiKGKD Bhachiopod {Linr/ula anatina). In- 

 terior of ventral (K.) and dorsal (/>.) valves, showing muBclo 

 scars, named as foUowa ; «., umbonal; p.s., parietal; t.m., 

 transmedian ; e.-L, externo-lateral ; 77».-?., medio-lateral ; c, 

 central; a.-^, autei'o-latural. Natural Bize, 



The Bnichiopoda possess a system of blood-vessels, with a contractile heart, 

 a distinct nervous system, and a jjair of excretory organs (nephiidia), which 



servo also for the transmission of the 

 7 generative products. Tlie sexes are 



usually separate, but Limjula is 

 hermap hrodite. 



The Brachiopoda are foimd in 

 seas all over the world, and usually 

 at depths of less than 100 fathoms, 

 but they have been dredged at a 

 depth of 2,900 fathoms. A few 

 (e.g., Limjula, Fig. 2) bury them- 

 selves in mud ; but most attach 

 themselves to rocks. They occur in 

 groat numbers wherever found. 

 Their shells, which are easily pre- 

 served, abound in strata of all ages, 

 so that a knowledge of them is of 

 great assistance to the geologist. 



The simplest form of Brachiopod 

 known occurs in the Lower Cambrian 

 rocks of America, and is called 

 Patcrina {Vvj,. T). Its valves are 

 oval in outline^ with ono side truncated by a straiglit hinge-line. Concentric 



PifJ. 0. — Internal organs of a Brachiopod 

 iRhynchoncUa psUtauca). p., peduncle; 

 D. v., dorsal valve, and V. V., ventral valve, 

 of the shell, which are broken away on one 

 side, exposing — L. , lophophore ; AT. , median 

 partition ; Oc, opsopluigus, leading from a 

 mouth between the coils of the lophophore 

 to the stomach, ■-'>.,' C, the coecuni, or blind 

 end of the gut, which has no auus. 



