184 THE PTEROPODA 



says (p. 46, PI. 3, figs. 33 — 34), only sometimes curved 

 to the left. A strong rib, running on the bottom of the 

 last whorl, so encircling the outer margin of the umbilicus, 

 resembles somewhat a similar one in L. helinna (Sars, 

 PI. 29, figs. \h — \c), though it does not at all project like 

 a keel on the outer surface of the shell. A remarkable 

 feature are the very conspicuous grooves, radiating from 

 the umbilicus (fig. 3). Boas notes only a few spiral striae, 

 encircling this umbilicus, of which I have failed to discover 

 any trace, while the radial sculpture is most distinct. 



The depressed spire, the wide umbilicus and the radial 

 sculpture make this species closely resemble L. helicina. 

 The more I regret not to have had any animal of Z. lesueuri 

 at my disposal, because, as Pelseneer (1888, p. 24) holds, 

 this species is not provided with the small lobe on the 

 anterior margin of the fin, which lobe on the other hand 

 is most distinct in L. helicina. 



Species 4. Limacina retroversa Fleming. 



(PI. 7, Figs. 4-5). 



Animals : 



Atlantic Ocean (Herlö, coast of Norway; 90 fathoms) September 22, '07, 



22 sp., Dr. C. Popta. 

 Atlantic Ocean (Gulf of Biscay), June '06, extremely common, Buitendijk. 



Most of the considerable numbers from the gulf of Biscay, 

 in an excellent state of conservation, were young specimens 

 (fig. 4), with a rather depressed spire, and only 4 whorls 

 in the spire. The whole surface of the extremely thin and 

 transparent shell is minutely and regularly striated in a 

 spiral direction ; this striation extends even to the aperture, 

 where the equidistant lines are readily visible, also in 

 adult specimens. While the height of the spire agrees with 

 that of -iSpirialis retroversus" Sars (p. 330, PI, 29, fig. 3a) 

 the striation is quite the same as in -èSpirialis halea'^ of 

 the same author. So the specimens from the gulf of Biscay 

 form a gradual transition between the two species of Sars, 



Notes from the Leyden IMuseum, Vol. XXIX. 



