164 



finer on the dorsal ridge and giving way to a minute punctatioa 

 in the region of the beak of each valve". This structure 1 found 

 to be correctly described. I will only remark, that the punctation in 

 the region of the beaks of the valves in many specimens may extend 

 over the whole jugal tract, sometimes even over a part of the 

 pleural tracts, so that the greater part of the middle valves may 

 be punctated, instead of lirate. As Issel's Figure (Man. of 

 Conchol. Vol. 14, PI. 20, Fig. 2) is correct, I only give a sche- 

 matic illustration of the sculpture of the middle valves (ribs black, 

 Fig, 12), It is very diflScult to give a clear and correct figure; 

 therefore I prefer a schematic illustration, 



In Fig. 13 is shown the sculpture of the middle valves of 

 meneghini. As seen the (black) riblets are broader and stronger 

 than in rissoi and their direction is more regular. They continue 

 their way on the lateral areas, but are irregularly broken by radial 

 grooves. These ribs are also found, though finer, on the jugal 

 tracts; the punctation is absent. Therefore the vs^hole sculpture 

 is stronger and more distinct. 



In dautzenbergi hovpever the v^hole lateral field is radiately 

 grooved (B'ig. 14), so that the longitudinal riblets are broken up 

 into more or less regular granules. Notwithstanding the direction 

 of the longitudinal riblets is still visible on the lateral areas, In 

 the extreme case the longitudinal riblets become thinner and feeble 

 and the radial sculpture stronger, so that the sculpture of the 

 lateral fields dominates. Between all these stages transitions occur; 

 in many cases it is very difficult to decide, whether we have to 

 do with rissoi, meneghini or dautzenbergi. The same diff"erence 

 between rissoi and menegJmn is shown in Pilsbry's Fig. 2 and 

 10 and Dautzknberg's letter (see Ancey's article) leaves no doubt 

 about the structure of the lateral areas of dautzenbergi. 



When we consider the length of rissoi^ we find in Pilsbry's 



-Manual: length 15 m. m., breadth 8 m.m.; for meneghini length 



25 m.m., breadth 13 m, m, (Man, of Conchol. Vol. 14, PI. 20, 



Fig. 8). Dautzbnbbrc does not say anything about the length of 



dautzenbergi; but as this forra was compared by him with mene- 



