SUB-KINGDOM IV.— BRACHIOPODA. 



LAMP SHELLS, ETC. 



By F. a. Bathek, M.A., F.G.S., Etc. 



The Biaohiopoda are marine auimals which, like some Mollusca, form ex- 

 ternal shells ; but they 

 differ from the Mollusca 

 in many points. 



The shell consists of 

 two valves, which lie on 

 the back and front of the 

 animal, not on its sides 

 as in bivalve Mollusca. 

 Each valve is symmetri- 

 cal in itself, which is very 

 rarely the case in Mol- 

 lusca ; but one valve is 

 nearly always larger 

 than the other. By this 

 larger valve the adult 

 animal is usually at- 

 tached to rocks or other 

 objects, either by the 

 direct growth of the 

 as is more usual, by means of a 



Fig. 1.— A SESSTtE Brachiovod {Crania) ; attaclied to a 

 piece of oyster-shell ; d.v., dorsal valve; v.v., ventral 

 valve; c.f/., exterior of dorsal valve; i.v., interior of 

 ventral valve. Twice natural size. 



valve to the rook (e,;;.. Crania, Fig. 1), or, 



Fig. 2. — A Pedunculate Brachio- 

 voii (.Lingula) The animal lives 

 in the mud (.in.) in a tube, the 

 bottom of which is lined with 

 cemented sand-grains {t.). The 

 shell (s.) is attached to this by a 

 peduncle {p.\ which can con- 

 tract, a. and ^-, the peduncle 

 outstretched; c, the peduncle 

 contracted; rf., the opening of 

 the tube from above. Greatly 

 reduced. 



Fig. 3.— Shell structure of, ^, a calcareous 

 slielled Brachiopod ; B, a horny shelled ; 

 w., mantle, wiiich sends processes O^.m.) 

 tlirough the prisms of carbonate of lime 

 that make up most of the sliell; p., outer 

 imperforate layer ; I., line of growth ; h., 

 horny layers; c, calcareous layers with 

 vertical canals. Greatly magnified. 



648 



