274 MANUAL OF ZOOLOGY. 



arms, or by means of spines developed in the ventral lobe of 

 the mantle. 



By Huxley the Brachiopoda are divided into two groups, 

 called respectively the Articulata and Inarticulata. In the 

 former the valves of the shell are united along a hinge-line, 

 the lobes of the mantle are not completely free, and the 

 intestine ends caecally. In this group are the recent Tere- 

 bratulidce and Rhynckortdlida. In the Inarticulata the valves 

 of the shell are not united along a hinge-line, the mantle- 

 lobes are completely free, and the intestine terminates in a 

 distinct anus. In this group are the Craniadce, JDiscinidce, and 

 LinguZidce. 



CLASSIFICATION OF THE BRACHIOPODA (AFTER DAVIDSON). 



CLASS BRACHIOPODA. 

 Fam. I. Terebratulida. 



Shell minutely punctate ; ventral valve with a prominent beak 

 perforated by a foramen for the emission of a muscular peduncle, 

 whereby the animal is fixed to some solid object. Foramen partially 

 surrounded by a deltidium of one or two pieces. Oral appendages 

 entirely or partially supported by calcified processes, usually in the 

 form of a loop, and always fixed to the dorsal valve. 



Genera. Terebratula (with Terebratulina, and IValdheimid), Tere- 

 bratella, Stringocephalus^ <2rY. 

 Fam. II. Thecididce. 



Shell fixed to the sea-bottom by the beak of the larger or ventral 

 valve ; structure punctated. Oral processes united in the form of a 

 bridge over the visceral cavity ; cirrated arms folded upon themselves, 

 and supported by a calcareous loop. 



Genus. Thecidium. 

 Fam. III. Spiriferidce. 



Animal free, or rarely attached by a muscular peduncle. Shell 

 punctated or unpunctated. Arms largely developed, and entirely 

 supported by a thin, shelly, spirally rolled lamella. 



Genera. Spirifer^ Spiriferina, Cyrtia, Athyris, &>c. 

 Fam. IV. Koninckida. 



Animal unknown. Shell free ; valves unarticulated (?). Oral arms 

 supported by two lamellae, spirally coiled. 



Genus. Koninckia. 

 Fam. V. Rhynchonellidce. 



Animal free, or attached by a muscular peduncle issuing from an 

 aperture situated under the extremity of the beak of the ventral valve. 

 Arms spirally rolled, flexible, and supported only at their origin by 

 a pair of short, curved, shelly processes. Shell-structure fibrous and 

 impunctate. 



Genera. Rhynchonella, Pentamerus, Porambonites, &>c. 

 Fam. VI, Strophomenida. 



Animal unknown ; some probably free, others attached, during the 

 whole or a portion of their existence, by a muscular peduncle. No 

 calcified supports for the arms. Shell with a straight hinge-line, 

 and a low triangular area in each valve. Shell-structure fibrous and 

 punctated. 



Genera. Orthis, Otthisina, Strophomena, and Lefihzna. 



