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



PTEROPODA. 



61 



Cephalobracliia nov. gen. 



Radula with very large teeth. Free border of the 

 median tooth forming a blunt point, with a series of 

 minute denticles on each side. 



Hook-sacs very large and forming, when evagi- 

 nated, a pair of strongly armed branches protruding from 

 the region of the head. 



No buccal cones. 



Cephalobrachia macrochaeta n. sp. 



PI. VII, fig. 53—58. 



Radula: Formula 3—1 — 3. Median tooth of the 

 genus-type. Lateral teeth horn-shaped without basal plates 

 (fig. 58, pi. VII, textfig. 49 A). The radula is, when 

 evaginated, placed at the top of a large cone, protruding 

 from the ventral side of the mouth (fig. 54, 55, 57 r. c). 



Hook-sacs of the family type with hooks of dif- 

 ferent sizes; the largest attain a length equal to one-fourth 

 of the fully extended body. When evaginated the hook- 

 sacs form two powerful arms diverging from near the 

 base of the radula-cone. 



As in the other representatives of this family there is 

 no jaw, but in its place, at the ventral side of the radula 

 is found a transverse lip formed by large glandular 

 cells. This lip forms a bow across the whole ventral side 

 of the proboscis (fig. 54, 57 /). 



The lateral lobes of the foot coalesce in front so as 

 to form a single lobe, fixed anteriorly and with a shallow 

 groove in its upper surface; posterior lobe small and 

 pointed. 



Wings large, with a narrow base and tapering also 

 towards the free end, the median part being the broadest. 



No gill. In one small specimen two parallel obli- 

 quely running lines surrounded the posterior part of the 

 body (fig. 53—54), but they were not observed in the 

 larger specimens, and are therefore probably larval cha- 

 racters. 



The visceral mass in all the specimens fills the 

 whole body. 



The skin is soft and transparent with minute scat- 

 tered tubercles. 



The three specimens are between 5 and 10 mm. in 

 length, but the largest individual (fig. 56) must have been 

 longer when fully extended. 



This new and peculiar species was taken during the 

 "Michael Sars" expedition at three northern stations and 

 all from deep water. 



Localities: St. 82 (48° 24' N, 36° 53' W). Depth: 500 metres. 

 „ 88 (45° 26' N, 25° 45' W). „ 750 „ 

 „ 92 (48° 29' N, 13° 55' W). „ 750 „ 



Dates: i3 h-°- 4 h 1910. 



Notobranchaeidae. 



Radula: Median tooth sickle-shaped, its concave 

 free border (generally) armed with denticles arranged in 

 a median and a pair of lateral rows (textfig. 52). 



Jaw: A row of small pointed spines on the ventral 

 wall of the buccal cavity. 



No acetabuliferous appendages. No lateral gill. 



This family was founded by Pelseneer (1888) for two 

 species, Notobrcinchaea inopinata and N. macdonaldi, the 

 characters of which were described and figured without 

 reference to the buccal organs. 



Characteristic of both species was the smooth spindle- 

 shaped body, pointed posteriorly and tapering anteriorly 

 towards the neck, which (the proboscis invaginated) was 

 narrower than the regularly rounded head. As mentioned 

 by Pelseneer these forms resemble Clione in outward 

 appearance, as well as in the fact that the visceral mass 

 does not reach the posterior end of the body. Other 

 distinctive characters were found in the shape of the 

 wings and foot. 



The genus Notobranchaea has been dealt with by 

 later authors, and new characters added to its diagnosis, 

 without however leading to a definite solution of the 

 question as to its systematic relations. 



Tesch (1904) describes a species from the "Siboga"- 

 expedition, which he identifies with N. inopinata. In 

 confirming the data given by Pelseneer he adds that 

 there are two pairs of buccal cones, and that the radula 

 has no median tooth. 



Meisenheimer (1905) in describing a specimen from 

 the "Valdivia"-expedition doubts the correctness of these 

 statements, for while he found no buccal cones, he ob- 

 served in the radula a series of very large median teeth. 

 Contrary to Pelseneer's description he found the visceral 

 mass in N. Valdlvlae filling the whole body. 



Buccal organs similar to those observed by Meisen- 

 heimer in N. Valdiviae were found by Pelseneer (1906) 

 in a new form, Fowlerina Zetosios, but he considered 

 this form to be nearly related to the Clionidae. 



As will be seen from the above statements considerable 

 confusion exists with regard to the systematic characters 

 and relations of Notobranchaeidae. 



I have among the "Michael Sars" material had an 

 opportunity of investigating species of Notobranchaea as 

 well as of Fowlerina, in both forms confirming the results of 

 Meisenheimer and Pelseneer (1906) with regard to the 

 buccal organs. The similarity of these organs in both 

 genera is in fact so great that I do not hesitate to com- 

 bine them into one family, in spite of the very obvious 

 difference in their outward appearance. To these two 

 genera I shall have to add the new genus Microdonta, 

 which, however, differs from them in essential characters. 



