SYSTEMATIC 169 



impossible to identify accurately. The largest shells were of 3-3! whorls, turbinate, with globose, 

 smoothly rounded whorls, the body whorl very large, and the aperture two-thirds the height of the 

 shell, ovoid and entire. There were no special sculptural features, except for the presence in the body 

 whorl of about six well-defined, close-spaced spiral cinguli, encircling the base of the whorl, well 

 below the point of greatest diameter. Numerous earlier stages of various sizes were present. Dimen- 

 sions of the largest individual: height c. 1-5 mm., diameter 1 mm. 



Superfamily Heteropoda 

 Family Atlantidae 



Atlanta peroni Lesueur 



1817 Atlanti peroni Lesueur, Journ. Ac. Nat. Sci. Philadelphia, 1. 



1852 Atlanta rosea Souleyet, Voy. de la Bonite, Zoologie, 11, 373, pi. 19, figs. 1-8. 



1949 Atlanta peroni Tesch, Dana Reports, xxxiv, p. 16, fig. 9. 



Table 2. Occurrence of Atlanta peroni 



This is the only heteropod represented in the present collection. It is an abundant and widespread 

 species, the commonest in Atlantic waters. Tesch (1949) discusses its distribution (p. 21). In the 

 North Atlantic it dwindles south of 20 N and appears to avoid equatorial waters. In the Benguela 

 material it was present on the southern line only, at three stations, WS 996, WS 997, WS 998. The 

 largest specimens measured 4-5-5 mm., and there were in several hauls an abundance of juvenile 

 shells, measuring up to 0-7 mm. 



Subclass Opisthobranchia 



Order PTEROPODA 1 



Suborder Thecosomata 



Superfamily Euthecosomata 



Family Limacinidae (=Spiratellidae) 



The continued use of the generic name Limacina in this paper may be held to require justification. 



Sherborn (1930) accepted Spiratella de Blainville (1817), as displacing Limacina as proposed by 



1 The single order Pteropoda is employed here to include both the thecosomatous and gymnosomatous pteropods, in keeping 

 with Thiele's system of classification (1931) which has been adopted throughout this section. It is not possible, however, to 

 regard such an order as a natural grouping. Pelseneer (1887, 1888) conclusively demonstrated the separate origins of the 

 two groups of pteropods, placing the Thecosomata at the end of the bullomorph series and regarding the Gymnosomata 

 as being derived from an aplysiomorph stock. He based his classification of 1906 on this view. The present writer (1954a) 

 has elsewhere pointed out— from a consideration of feeding and digestive mechanisms in the pteropods— that the reversion 

 by Thiele and by Hoffmann (1938) to a single order Pteropoda cannot be defended on strict phylogenetic grounds. 



