THE NAUTILUS. 69 



shapes in the interim. Some of these ova resembled dumb bells in 

 shape (except that the two balls were in close juxtaposition). 

 Close observation showed that on the side of the spherical vitellus 

 would appear a slight bump or projection. This would slowly grow 

 until it had become as large as the remainder of the yolk, thus pro- 

 ducing the dumb bell, apparently the fluid contents of the yolk would 

 pour itself from one ball into another, and a motion similar to that 

 of the well known Amoeba would result. 



The other case was that of the ova of Anodonta imbecilUs Say, 

 which were in the mulberry stage. These were revolving about an 

 axis, making in some instances six complete turns per minute, while 

 the axis was fixed for each individual, the direction of this axis bore 

 no relation to anything that I could see, but were in every direction. 

 Some were horizontal, others perpendicular and many oblique. 



This revolution was confined to the inside of the shell. The egg 

 as a whole remaining unmoved, neither the cause or object of this 

 rotation could be noted or conjectured by me. Possibly when packed 

 together in the marsupium, the motion would influence the shell, and 

 so in a measure prevent congestion in the narrow gill passages. 



A solution of salt would in a minute or two cause a visible con- 

 traction of the vitellus, and the stoppage of the motion. Being 

 curious to know if alcohol would stimulate their motions I placed a 

 drop on the slide. In an instant an appearance resembling a violent 

 effervescence took place, and at its close every egg-shell had burst 

 open\ Apparently the endosmosis had so far exceeded the exosmosis 

 as to burst the membranes. 



Frierson, La., August, 1906. 



SPHJEKIUM HENDERSONI N. SP. 



BY V. STERKT. 



Mussel large, almost equipartite, well inflated ; superior margin 

 curved, with slightly marked rounded, or no angles where passing 

 into the supero-anterior and posterior slopes which are slightly 

 marked; scutum and especially scutellum distinct; anterior and 

 posterior ends rounded, the latter scarcely drawn downward ; beaks 

 near or in the middle in half-grown and adult specimens, markedly 



