BY E. M. JOHNSTON, F.L.S. 



117 



foliaceous, and with a prominent beak ; ligamental 

 cavity triangular or elongated ; hinge toothless ; 

 structure sub-nacreous, laminated with prismatic- 

 cellular substance between the margins of the laminse. 

 Dist. — Tropical and temperate seas, Norway, Black 

 Sea, Australasia, etc. 



BRACHIOPODA. 



(cii.) Family Terebratuxims. 

 Shell minutely punctate ; usually round or oval, smooth or 

 striated ; ventral valve with a prominent leak, perforated 

 near or at the apex, and attached by a portion of the 

 valve itself ; hinge with two curved teeth ; dorsal 

 valve with a depressed umbo, a prominent cardinal 

 process between the dental sockets, and a slender 

 shelly loop. (Lamp shell.) 



G-enus Waldheimia. (714.) 

 Shell smooth or plaited, dorsal valve frequently impressed; 

 foramen complete ; loop elongated or reflected ; septum 

 of smaller valve elongated. Dist. — Norway, West 

 Indies, Java, Australia, California, Cape Horn ; low 

 water, 100 fathoms. 



Genus Keaussia. (715-716.) 

 Shell small, transversely oolong ; hinge-line nearly straight ; 

 beak truncated, laterally keeled ; area flat ; foramen 

 larr/e, deltidum rudimentary ; dorsal valve longitudinally 

 impressed, furnished inside with a forked process, 

 rising nearly centrally from the septum ; interior 

 often strongly tuberculated. The Apophyses are 

 sometimes a little branched. Dist. — S. Africa, Sydney, 

 New Zealand ; low- water to 120 fathoms. K. rubra, 

 Pallas. 



DESCRIPTIVE TEEMS. 



Explanation oe Teems Commonly Used in Describing 

 the External Chaeactees and Eorms oe Vaeious 

 Kinds chf Shells. 



Shells are said to be external when the animal is contained 

 m them, and internal when they are concealed in the mantle ; 

 the latter, with many species devoid of shelly covering, are 

 termed naked mollusca. The greater number of shells have 

 but one shell (usually a closely-set spiral tube or cone,) and 

 are termed univalves ; the others are mostly composed of two 

 valves (bivalve) hinged together, generally under the beak or 



