3 20 
The Ohio Naturalist. 
[Vol. Ill, No. 1 
*ON A VISUAL AREA IN LAMPSIDA VENTRICOSUS 
F. L. Landacre. 
The following observations were made on Latnps'da Ventri- 
cosus (Unto subovatus), with a view to determining the exact 
nature of what appears to he a visual area on the posterior mantle 
lobe. 
This particular clam attracted the writer's notice during 
several years while collecting material for laboratory use. The 
females while carrying the young glochidia, in the fall, frequent 
the ripples rather than the quiet portions of the stream as most 
clams do: and always lie in the gravel with the long axis hori- 
zontal. In addition to these two peculiarities, ventricosus almost 
always has two large frill like appendages on the hinder edge of 
the mantle lobe, and these are usually found moving in the run- 
ing water. These frills are from one inch to an inch and a half 
long, and bear a prominent eye like spot on the dorsal portion. 
The frill is widest on the ventral portion and gradually merges 
into the mantle on its dorsal surface. The free edge of this frill 
bears tentacles which are well pigmented. 
The dark spot on the dorsal portion is borne on a light field. 
The waving of the frill, which at first appears to be due 
to the current, was found, after specimens were kept under obser- 
vation in the laboratory, to be quite regular in quiet water, and 
to occur at the rate of from thirty to fifty contractions per minute. 
The purpose of these movements seems to be to furnish fresh 
water to the young in the gills. These are frequently so distended 
with young that the clam cannot close its shell at all. It can 
hardly serve the purpose of distributing the young as they are 
carried until spring. 
The animal, while moving its mantel lobes in the water, 
bears a striking resemblance to a bit of- grass attached to a half 
submerged stone. This protective resemblance can hardly account 
for the peculiarity, and, as suggested above, it is probably respir- 
atory in function. 
The animal is much more active on bright days, and was 
observed to retract its mantle when a shadow was thrown on it. 
This suggested that there must be a visual epithelum somewhere 
on the mantle lobe. 
The attempt to demonstrate the connection of the nerves 
running to the posterior mantle region with the epithelial cells 
was not successful, although both Golgi, and Vom Rath methods 
were used. The histology of the pigmented area, especially the 
eye like spot was carefully worked out, and while the actual con- 
Read before the Ohio Academy of Science. Columbus, Ohio, 1897. 
