410 Dr. J. E. Gray on some Families of Bivalve Shells. 



by a central line, and what is usually the outer dependent gill is 

 bent up against the upper part of the side of the body, the strise 

 radiating from the central attachment; hence in Solenomya they 

 have been called pinnate. See Hancock, Ann. and Mag. N. H. 

 1853, vol. xi. t. 3 & 1. 11. In Lucinidce there is only a single gill 

 on each side, the outer being absent, or the two are soldered 

 into one. 



The gills oiNucula and Pandora are somewhat intermediate in 

 appearance between the pinnated gills and the more common 

 form, and the transition from the Nuculce to the Area is easy. 



Order I. Veneracea. 



Mantle with two more or less elongated siphonal openings. 

 Gills short, not produced into the inhalant or lower siphon. 

 Siphons often more or less separate, under the hinder adductor 

 muscle. 



I. Foot compressed : animal crawling. 



1 . Cardinal teeth diverging, central bifid. 



A. Siphons more or less united, short ; cartilage of hinge external, 

 marginal. 



1. Venerida, Syn. B. M. 1842, 74; P. Z. S. 1847, 183; Ann. 

 and Mag. N. H. 1853, 36. 



2. Cyprinida, Ann. and Mag. N. H. 1853, 36. 



3. Glauconomida, Ann. and Mag. N. H. 1853, 36. Siphons 

 united at the base ; pedal opening small. 



4. Petricolidce, Ann. and Mag. N. H. 1853, 36. Siphons 

 separate nearly to the base, pedal opening small. Perhaps allied 

 to Tellinidce. 



5. Corbiculada, P. Z. S. 1847, 184; Ann. & Mag. N. H. 1853, 

 36. Cyrenadffi, Syn. B. M. 1842, 75. 



6. Cyrenelladce, Ann. and Mag. N. H. 1853, 37. For the cha- 

 racters of these families see the 'Annals.' 



6*. Mysiada. Pedal opening moderate, inferior. Siphons 

 none ; anal opening linear, with two semilunar lateral valves, in- 

 halant small, round, fringed. Gills two on each side ; lips four, 

 moderate. Foot compressed, lanceolate. Hinge with two diver- 

 ging bifid teeth ; no lateral teeth. Cartilages linear, marginal. 



1. Mysia=Diplodonta. 



7. Astartidce, P. Z. Soc. 1847, 19. Crassinadse, Syn. B. M. 

 1842, 80. Pedal opening elongate. Shells covered with a thick 

 brown periostraca. Cardinal teeth broad, triangular, hinder lateral ; 

 of the left valve double. 



1, Astarte. 2. Gypricardia, sp. according to D'Orbigny. 



