10 
PROCEEDINGS OF THE ACADEMY OF 
gin; alate expansion gradually flattened ; anterior end abruptly rounded, exca¬ 
vated by a lunuliform area in front of the beaks ; posterior end rounded below, 
truncate above. Surface covered by fine, rather regular, sharp, concentric 
striae; the alate expansion bears also faint traces of two or three furrows 
diverging from behind the beak. r 
Length -31 (100); height *22 (71); thickness of right valve -10 (32) ; angle 
between hinge-line and umbonal ridge 35°. 
This little species closely resembles A. arguta , Phill., sp., var. de Kon., 
(Anim. Foss., pi. iii. fig. 12.) The beaks, however, are still more terminal than 
in that variety, and the lunette is not so sharply bounded. Area arguta , var., 
is from carboniferous limestone—Vise. Though the dental characters of the 
present species have not been observed, it can scarcely prove to be anything 
but an Area or Macrodon. 
MACRODON, Lycett. 
Macrodon cochlearis, n. sp.—Shell of moderate size, rather ventricose, 
length equal to twice the height; beaks subterminal, flattened, incurved. 
Ventral border straight, or slightly sinuate in the middle, symmetrically 
curved toward the extremities ; posterior extremity truncate from the hinge¬ 
line one-third its width; anterior extremity most projecting above the mid¬ 
dle, excavated above by a small deep lunette; dorsal line straight, nearly as 
long as the shell, not inflected ; posterior cardinal extension with feeble in¬ 
dications of one or more lateral teeth. Surface finely striated concen¬ 
trically. 
Length *88 (100); height *44 (50); length of anterior end *16 (19); of 
posterior end *72 (81) ; thickness of left valve *18 (22). 
Resembles M. parvus , White and Whitefield, but, besides its larger size, it 
is much less ventricose, especially in the posterior half, and has not the 
conspicuous muscular pits of that species. 
NCJCULA, Lamarck. 
Nucula microdonta, n. sp.—Shell small, transversely oblong; height 
equal to two-thirds the length ; beaks small, somewhat incurved, but little 
elevated above the hinge-line, about one-third the length from the short end. 
Ventral border rapidly curved, and regularly so to the vicinity of the long 
end, where it is slightly sinuated, from which point a shallow groove extends 
up nearly to the beak. Dental plates but little angulated between the beaks ; 
the larger bearing near its outer margin 10 or 12 minute transversely tuber¬ 
cular teeth, and the shorter 4 or 5. Teeth not distinguishable to the beaks, 
but no cartilage pit seems to be present. Anterior muscular pit oblong, sur¬ 
mounted by a large pedal scar. Shell most ventricose in the middle. No 
surface markings discernible. 
Length *47 (100); height -32 (68); length of short end *18 (38); of long 
end *29 (62); thickness of both valves *18 (38). 
This little species is readily distinguished from N. lowensis, and most 
others of this age, by its very small teeth and the absence of the usual 
nuculoid outline. 
Ranges from bed No. 5 into the base of the Burlington limestone. 
LED A, Schumacher. 
Led a saccata, n. sp.—Shell very small, transversely elongate, rostrate at 
the longer extremity; obtuse, ventricose and saccate at the other. Beak 
abruptly, though moderately drawn out, and but slightly incurved. Ventral 
side strongly curved, becoming nearly straight toward the rostral extremity. 
Dorsal region deeply excavated for an escutcheon on the longer side of the 
beak ; hinge plates bearing each six or seven teeth. Greatest thickness of shell 
between the beaks and the middle. Pit of adductor of short end very deep 
[Jan. 
