320 The Ohio Naturalist. [Vol. Ill, No. 1, 



*ON A VISUAL AREA IN LAMPSIDA VENTRICOSUS 



F. L. Landacre. 



The following observations were made on Lampsida Veyitri- 

 cosus {^Unio subovatns ), with a view to determining the exact 

 nature of what a})pears to be a \-isnal 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, \entricosus almost 

 always has two large frill like appendages on the hinder edge of 

 the mantle lobe, and these are usualh- found moving in the run- 

 ing water. These frills are from one inch to an inch and a half 

 long, and l)ear a prominent eye like spot on the dorsal portion. 

 The frill is widest on the ventral portion and gradualh' 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 thirt>- to fifty contractions per minute. 



The purpose of these movements seems to be to furnish fresh 

 water to the yovuig in the gills. These are frequently so distended 

 with young that the clam cannot clo.se 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 nuich more active on bright days, and was 

 ob.served to retract its mantle when a shadow was thrown on it. 

 This suggested that there nmst be a \-isual 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 l)oth Golgi, and \V)ni 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. 



