ANATINIDA. 149 
cylindrical, gaping at both extremities, greatly posteriorly ; 
beaks small, narrow, pointed, nearly contiguous, not elevated 
and but little curved; anterior muscular impressions oval or 
pyriform, posterior rounded; pallial impression indistinct. 12 
sp. Liassicand Jurassic. Europe. MM. oblonga, Agass. (eviii, 69). 
MAcTROMYA, Agassiz, 1842. (Plectomya, Loriol.) Shell swollen 
or globular, very thin, striate; hinge without teeth—at least 
none are visible on the internal casts ; ; an internal rib proceeds 
from before the beaks obliquely to the anterior margin. Creta- 
ceous and Jurassic; Europe. JZ. rugosa, Agass. (cvil, 46). 
SEDGWIcKIA, M’Coy, 1844. 
Distr.—S. attenuata, M’Coy. Carb.; Europe. Sil.; N. Y. 
Shell elongated, inequilateral, anteriorly rounded and shorter, 
posteriorly subtruncated, moderately tumid, with incurved beaks, 
anterior half of the surface ornamented with concentric sulca- 
tions, becoming obsolete posteriorly, hinge edentulous. 
PYRENOMUS, Hall, 1852. Elongated, inequilateral, anteriorly 
rounded, posteriorly attenuated and produced, concentrically 
striate-sulcated on the surface; beaks tumescent, anterior 
muscular impression deep, subanterior (posterior unknown) ; 
hinge apparently without teeth ? 
P. cuneatus, Hall (exx, 15). Clinton group (Middle Silurian) 
of North America. Perhaps belongs in Nuculide. 
LEPTODOMUS, M’Coy, 1844. Shell oblong, somewhat trape- 
zoid, tumid, very thin, anteriorly rounded, beaks subanterior, 
posteriorly subtruncate and gaping, concentrically sulcated ; 
beaks incurved, with a somewhat excavated lunule below; hinge 
without teeth, the posterior hinge- line more or less straight, 
muscular and. pallial impressions faint. LZ. fragilis, M’ Coy. 
The species are all paleozoic; those with a median suleus 
extending from the beaks to the ventral edge seem to be more 
correctly referable to Grammysia; the typical forms greatly 
resemble some Cypricardiz, but are readily distinguished from 
them by their thin shells. 
TyLeRIA, H. and A. Adams, 1854. 
Distr.— T. fragilis, H. and A. Ad. (eviii, 70). Mazatlan. 
Shell oblong, rounded in front, gaping behind, covered by a 
very slight epidermis; valves thin, nearly membranaceous ; 
cartilage inserted in a spoon-shaped hollow; interior of shell 
with a laver of carbonate of lime between the spoon-shaped 
hollow and the anterior edge; pallial line with a profound sinus. 
ANATINA, Lamarck, 1809. 
EKtym.—Anatinus, pertaining to a duck. Lantern-shell. 
Syn.—Laternula, Bolten, 1798. Auriscalpium, Muhlf., 1811. 
Rhynchomya, Agass. 
