464 Benjamin Sharp 



In Saxidomus NiitaUii (Conrad) the siphon is well developed and 

 darkly pigmented at the extremity. 



Farn. Tellinidae. 



Will states that Tellina is one of the forms, which have well 

 developed eyes. I can safely say from the speeimens, that I have exa- 

 mined of Tellina tenta , that I found not only no trace of eyes, but also 

 no pigment deposit present. 



Farn. Mactridae» 



With Mactra solidissima I have had the opportimity to experiment 

 and found the sanie sensitìveness to light and shadow that I have found 

 in other species. with which I have experimented. 



The siphon is well developed, not very long but quite robust. The 

 externa! mouths of the siphon are densely fringed with tentacles from 

 1 mm to 2,5 mm in length, these tentacles are short and thick and really 

 have more the appearance of cones tlian of tentacles. 



When sections of tbis part are made and examined , we find no 

 essential difference from those already described. The cells contain a 

 brownish black pigment and are about the same length as those of 

 Solen (fig. 9) , the pigment being deposited next to the well marked 

 and transparent cnticle. The pigmented cells bere seem as in the pre- 

 ceding form to bave a tendency to form into grooves or at the bases 

 of the tentacles for protection , this being a step in advance of those 

 forms , where the pigmented cells are simply scattered in the general 

 epithelium. 



In the other species that I have examined, Mactra ponderosa , the 

 grooves were pale , but distinct at the base of the tentacles , and the 

 siphon tolerably well developed. 



Farn. Myacidae, 



In Mya arenaria the siphon is from one to one and a half times 

 the greater length of the shell : the whole is covered with a compara- 

 tively thick cuticula, which is thrown into innumerable folds, when the 

 siphon is contracted. This cuticula is a continuation of the cuticle, 

 which Covers the thick border of the mantle and the newly formed bor- 

 der of the Shell. The cuticula is thinnest near the external end of the 

 siphon. 



The end of the siphon is quite black and pigment in spots occurs 

 for quite a distance below the end. The mouths of the siphons are sur- 



