212 M. C. Mereschkowsky on some 



had the opportunity of examining, is in the form of a wide, 

 somewhat inflated vase, rounded or terminating in a point at 

 the bottom, thus forming, as we shall see, two distinct varie- 

 ties. At the upper part it narrows suddenly, forming a wide 

 but not very long neck, the margins of which are not turned 

 out. In the variety that 1 have observed in the Black Sea, 

 the neck is a little narrower relatively to the total width of 

 the carapace (PI. XII. fig. 2) , which causes the neck to be more 

 accentuated ; while in the other variety, from the Bay of 

 Naples, the neck is almost as wide as the carapace (PI. XII. 

 fig. 1), as may be seen by comparing the two figures here 

 given. 



The neck and the upper part of the carapace itself are 

 adorned with slight rings, which are nothing but circular 

 elevations or thickenings of the chitinous substance of the 

 carapace. These circular striae are four or five in number ; 

 and their arrangement is slightly different in the two varieties 

 of the species that I have observed. In one of them, that 

 from the Black Sea (fig. 2), the neck is ornamented with 

 three rings, while the actual body of the carapace has only 

 two ; in the Neapolitan variety, on the contrary, there is 

 only a single ring upon the neck, the others being placed upon 

 the first third of the carapace itself (fig. 1). But the principal 

 difference which distinguishes the two varieties is the form of 

 the bottom of the carapace. Whilst in the specimen that I 

 observed in the Black Sea the bottom is regularly rounded 

 (fig. 2), that of the Neapolitan variety presents at the pos- 

 terior extremity a rather long and regularly conical point. 

 We should thus have two local varieties : — 



1. \&x. poTitica, with the bottom of the carapace rounded. 

 Log. Black Sea, Crimea, Livadia. 



2. Var. nea/politana^ with the bottom terminating in a point. 

 Log. Bay of Naples. 



This species, which is very easily distinguished by its form 

 from all the other known species, is a marine species charac- 

 terizing the fauna of the whole Mediterranean. It does not 

 appear to be very rare ; for I have found it in two different 

 localities, namely the Black Sea and the Bay of Naples, 

 although under somewhat different forms in the two places. 

 Unfortunately I did not once happen to meet with the living 

 animal ; I have never seen more than the carapace. 



The following are some measurements of this species (var. 

 ponticaf: — 



millim. 



Total length of tbe carapace 016 



Maximum breadth 0013 



Lenirth of the neck 0-002 



