113 
nor very deep ; between this part and the beaks the surface is 
blackish and transversely wrinkled ; posterior and anterior surface 
of the valve longitudinally striated, with the exception of the an- 
terior cordate hinge-margin, which is flattened and covered by a 
thick stratum of compact sand ; anterior tip equally arcuated above 
and below ; within iridescent, brilliant, striated as on the exterior 
surface, edge crenate. 
Breadth nearly half an inch; length more than one-fifth of an 
inch. 
This species differs from the M. discors^ and M. lateralis, nob., 
not only by its very singular habit, but also by its flat and per- 
fectly heart-shaped anterior margin; the regular and equal curva- 
ture of its anterior extremity ; the narrower interval between the 
anterior and posterior striated surfaces, and the more profound and 
less dilated basal contraction, 
PI. xix, fig. 2. M. opifex imbedded in its mound, a. External view 
of a valve. 6. Internal view of a valve, (all enlarged.) 
[Included on pi. 70. — En.] 
[J. A. N. S., vol. V. p. 122, et seqq., Sept. 1825.] 
Lymneus modicelles. — Shell blackish, not elongated : whorls 
rather more than four, convex ; suture deeply impressed ; apex 
acute ; aperture very regular, the labium and labrum being sub- 
equally curved ; the fold of the columella rather slight. 
Total length, seven-twentieths of an inch ; breadth one-fifth ; 
length of the aperture orge-fifth. 
Smaller than any of the species I have hitherto described. It 
was found by Dr. M‘Euen at Oswego, on the Susquehanna river 
near the State of New York. 
Lymneus obrussus. — Shell oblong, rather slender, pale yel- 
lowish testaceous ; whorls five, slightly rounded ; apex acute : 
suture deeply impressed ; aperture not dilated, within pure white ; 
columella with the sinus of the fold very obvious. 
Lister, pi. fig. 8 ? 
Total length nine-twentieths of an inch ; aperture one-fourth ; 
breadth nearly one-fifth. 
All the individuals that have occurred were covered with an 
earthy slime. They inhabit a small rivulet below the fish-ponds 
at Harrowgate, the seat of my friend Mr. J. Gilliams. 
