134 SAXICAVID^. 



they are vertical cylindrical cavities, one and one-half inches in 

 diameter and twelve or more deep ; the animal holds fast by the 

 expanded end of its foot. 



MESOPLEURA, Conrad, 1861. Valves with an interior rib cross- 

 ing from the beak to the opposite margin. 3 sp. TJ. S., Java, 

 California. S. centralis^ Say. Atlantic Coast of U. S. 



NOVACULiNA, Benson. (Loncosilla, Raf.) Shell oblong, plain ; 

 epidermis thick and dull ; pallial sinus rather small ; anterior 

 pedal scar linear. 3 sp. India, China. In the mud of river- 

 estuaries. N. conatricta, Lam. (cv, 88). 



SOLYMA, Conrad. Shell ovately elongated, thin, equilateral, 

 ventricose ; right valve with two direct approximate teeth under 

 the beak. Type, S. lineolatus (cv, 89). Cretaceous; N. J. Con- 

 rad states that the genus is allied to Leptosolen, though as to 

 form it rather appears to exhibit greater relation to some Telli- 

 nidse, and as regards the hinge-teeth of the right valve it is 

 allied to Solecurtus. 



Macha, Oken, 1815. 



Syn. — Solecurtus, Blainv. (pt.). Psammosolen, Risso. Cyrto- 

 solen, Herrm. 



Distr. — 8 sp. West Indies, Mediterranean, East Indies. M. 

 strigillata, Linn, (cvi, 15). 



Shell transversely oblong, compressed, rounded and gaping at 

 the extremities, obliquely striate, more or less invested with an 

 epidermis, beaks subcentral, margins nearly parallel ; hinge with 

 two diverging primary teeth in each valve ; lig:iment prominent; 

 anterior muscular impression lobed ; pallial impression deeplj- 

 sinuated. 



Siphons very large, united at the base ; the branchial orifice 

 fringed, anal free. The animal is very large and not entirely 

 retractile within the shell. Usually lives buried in sand, coral- 

 line zone. 



AZOR, Gray, 184*1. Valves smooth, covered by an epidermis. 

 5 sp. Europe, Philippines. M. coarctata, Gmel. (cvi, 16). 



(Myacea.) 



Family SAXICAVIDJE. 



Shell equivalve, thick, gaping at the extremities; hinge with 

 a single cardinal tooth ; ligament external, prominent, solid ; 

 inserted in a nj'mphal callosity ; pallial impression irregular, 

 sinuous. 



Animal elongated, symmetrical; mantle-lobes united, with a 

 small opening for the digitiform foot ; siphons large, elongated, 

 covered with a thick skin, the orifices fringed. The Saxicavidae 

 live in sand, mud or soft rock, excavating the latter. There are 

 but few living species, but the extinct forms are numerous. 



