ATLANT. DEEP-SEA EXPED. 1910. VOL. III]. 



PTEROPODA. 



I It 



Fig. 3. Radula of Peraclis diversa. int., l.t., r.t. as in fig. 2 



The most complete description of this species is given 

 by Locard, who, however, had only the empty shells at 

 his disposal. His description 1 ) and figures agree so well 

 with the specimens from the "Michael Sars" Expedition 

 that I have no doubt of their identity, although Locard 

 as well as Monterosato describe their shells as having 

 a smooth surface, while the "Michael Sars" specimens 

 show fine hexagonal reticulation, all over their shells 

 (pi. I, fig. 1). This reticulum may be destroyed very soon 

 after the death of the individuals, and may therefore not 

 be found on deposit shells. 



As already mentioned by Locard, the ridges radiating 

 from the suture are on the last half-whorl of the shell 

 bordered by another ridge parallel to the suture and 

 increasing in rigidity towards the outer lip of the shell 

 (pi. I, fig. 1 b). When this lip is broken, the ridge pro- 

 trudes like a spine, very much like that of Peraclis 

 bispinosa Pelseneer, and if by a further growth of the 

 shell this spine should prove to form a constant feature 

 of the lip also in P. diversa, the two species ought to 

 be considered as identical. 



So far as can be seen from the short description 

 given by Pelseneer (1906) of his P. brevispira, that 

 species also seems to be identical with P. diversa, the 

 more so because the lateral teeth of the radula have the 

 same characteristic shape in both forms (textfig. 3). The 

 only reason why their identity should still remain question- 

 able is the fact that Pelseneer does not mention the 

 reticulum of the shell, although he must have had fresh 

 specimens at his disposal. His description being, however, 

 rather fragmentary too much weight ought not to be 

 attached to this fact. 



As mentioned above the P. reticulata of Meisenheimer 

 (1905) has both reticulum and ridges, and is probably 

 identical with our species. 



A characteristic feature of the mantle-margin of P. 

 diversa is the existence of a big apparently glandular 

 lobe (textfig. 1 B, and pi. I, fig. 2 gl. I.) protruding from 

 its left side. The denticled border of the lateral teeth is 

 not protruding as in P. reticulata, but has a slightly 

 concave outline. 



') I have not been able to find the umbilicus mentioned but not figured by Locard. 



