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



PTEROPODA. 



63 



Fig. 53. Radula of Notobrancliaea tetrabranchmta. 



terised by the spindle-shaped Clione-Wke body. Tesch 

 (1904) and Meisenheimer (1905) referred new species to 

 this genus, but from my study of the "Michael Sars" 

 material I fully agree with Meisenheimer that according 

 to Tesch's description the "Siboga" species does not corre- 

 spond with that of Pelseneer and that in fact it does not 

 belong to this genus. 



In the material from the "Michael Sars" expedition 

 the genus Notobranchaea is represented by two individuals 

 helonging to one species new to science: 



Notobranchaea tetrabranchiata n. sp. 



PI. VIII, fig. 61-62. 



In outward appearance this species very much resembles 

 the original species of Pelseneer, and therefore also Clione 

 limacina. The pointed posterior part of the body is trans- 

 parent and empty, as in the forms just mentioned, but 

 at the same time it is distinguished from them by having 

 tetraradiate posterior gill, whereas the gill in Pelseneer's 

 two species is triradiate and Clione has no gill at all. 



Radula: Formula 6—1— 6 (textfig. 53). The denticles 

 of the median teeth [are somewhat irregularly arranged 



within each group, while the relation between lateral and 

 median groups is always the same as mentioned for the 

 genus. Lateral teeth large, hook-shaped, each hook when 

 fully developed consisting of regularly arranged substances 

 varying in transparency. 



Jaw: A row of 14 spines each forming a hollow 

 cone (textfig, 54). 



Hook-sacs small, shallow, with short and slender 

 hooks; the muscular apparatus of the hook-sacs slightly 

 developed. (Textfig. 55.) 



Foot: Lateral lobes closely approximated anteriorly 

 and diverging posteriorly so as to form two sides of an 

 equilateral triangle. The median tubercle repeats the same 

 figure in miniature. Posterior lobe narrow and pointed, 

 its front side forming a longitudinal groove. 



Wings narrow at the base and broadly truncated 

 at the free end. 



Posterior gill consisting of 4 crests meeting in a 

 point at the posterior end of the body. 



A. 



B 



Fig. 54. Jaw of Notobranchaea tetrabranchiata. 



Fig. 55. Notobranchaea tetrabranchiata. A. Hook-sac. 

 B. Buccal organs (r radula; j. jaw; h. hook-sac). 



