134 SAXICAVIDA. 
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, 1867. Valves with an interior rib cross- 
ing from the beak to the opposite margin. 38 sp. U.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. 38 sp. India, China. In the mud of river- 
estuaries. NV. constricta, Lam. (cv, 88). 
soLyMA, Conrad. Shell ovately elongated, thin, equilateral, 
ventricose ; right valve with two direct approximate teeth under 
the beak. Type, S. lineolatus (ev, 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- 
nidee, and as regards the hinge-teeth of the right valve it is 
allied to Solecurtus. 
Macua, Oken, 1815. 
Syn.—Solecurtus, Blainv. (pt.). Psammosolen, Risso. Cyrto- 
solen, Herrm. 
Distr.—8 sp. West Indies, Mediterranean, Hast Indies. J. 
strigillaia, Linn. (evi, 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; ligament prominent; 
anterior muscular impression lobed; pallial impression deeply 
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, 1847. Valves smooth, covered by an epidermis. 
5 sp. Kurope, Philippines. JZ coarctata, Gmel. (evi, 16). 
( Myacea.) 
Famity SAXICAVIDA. 
. Shell equivalve, thick, gaping at the extremities; hinge with 
a single cardinal tooth; ligament external, prominent, solid ; 
inserted in a nymphal 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 Saxicavidee 
live in sand, mud or soft rock, excavating the latter. There are 
but few living species, but the extinct forms are numerous. 
