64 



KR. BONNEVIE. 



[REP. OF THE "MICHAEL SARS" NORTH 



Skin: smooth, unpigmented. 

 Size: 6 — 8 mm. in length. 

 Localities: St. 10: 45° 26' N, 9° 20' W. Surface. Date: 

 i9/ 4 _ 21/4 1910. 1 individual. 

 St. 92: 48° 29' N, 13° 55' W. Depth 150 

 metres. Date: 23 A— 24 / 7 1910. 1 individual. 

 In both individuals the penis is evaginated, forming 

 a broad folded lobe, along the margin of which a narrow 

 groove leads upjto a"short finger-like protrusion. 



Fig. 56. Radula of Fowlerina hjortii, n. sp 



Fowlerina Pelseneer. 



This genus was founded by Pelseneer (1906) upon 

 some specimens contained in the Biscayan plankton, the 

 outward appearance of which is very different from that 

 of Notobranchaea. (See pi. VIII, fig. 63—68.) 



Instead of the slender spindle-shaped body of Noto- 

 branchaea, we find in the genus Fowlerina forms with 

 relatively broad cone-shaped bodies, the apex of the cone 

 being represented by the posterior end of the body and 

 the base by the broad neck-region, which in contracted 

 individuals is folded so as to conceal more or less com- 

 pletely the head as well as the foot and wings. 



This difference in the shape of the animals in the 

 two genera is caused by the very different development 

 of the proboscis. In Notobranchaea this apparatus con- 

 sists of nothing but an invaginated cone, the walls of 

 which carry the characteristic buccal organs, while in 

 Fowleiina the proboscis forms a large and complete system 

 of muscular layers surrounding each other like the cylin- 



1 ) I cannot agree with Pelseneer that this pair of tentacles should 

 I been able to find more than one pair of posterior tentacles. 



ders of a telescope, so that every stage in its evagination 

 imports to the animal a different and characteristic ap- 

 pearance. The illustrations, fig. 63 — 68, will convey a 

 better idea of this gradual change in external appearance 

 than a verbal description. 



Considering the great difference in outward appearance, 

 it is surprising to find the buccal organs, radula, jaw, and 

 hook-sacs, of exactly the same type in both Notobranchaea 

 and Fowlerina. Their conformity in this important point 



is, as already pointed out, my 

 reason for including the genus 

 Fowlerina in the family Noto- 

 branchaeidae, instead of fol- 

 lowing Pelseneer in placing it 

 among the Clionidae. 



Radula: Median tooth 

 of the family type; the arran- 

 gement of the denticles like 

 that in the genus Notobran- 

 chaea. Lateral teeth hook- 

 shaped, increasing in size to- 

 wards the median line of the 

 radula. 



Jaw: A row of conical 

 spines continued .on each side 

 by a series of small single 

 spines forming curved lines 

 towards the hook-sacs. 



Hook-sacs shallow, with 



short but strong hooks and a 



strong muscular apparatus. A 



group of large clear cells is found at their dorsal margin. 



Proboscis: A complex organ, the mouth opening 



towards the dorsal side. 



Tentacles: Two pairs, the anterior pair covered 

 with groups of large club-shaped cells; 1 ) both pairs may 

 be invaginated within the proboscis-wall (pi. VIII, fig. 67). 

 Foot without a median tubercle. 

 In the "Michael Sars" material this genus is repre- 

 sented by six individuals belonging to one species, new 

 to science. 



Fowlerina hjortii n. sp. 



PI. VIII, fig. 63—68. 



Radula: Formula 6—1 — 6. The hook-shaped lateral 

 teeth are simpler than those of Notobranchaea tetrabran- 

 chiata, looking very much like a foot with a slipper. 

 (Textfig. 56). 



Jaw: A median row of 14 spines continued on each 

 side by a series of 7 or 8 small single denticles (textfig. 

 57—58). 

 be considered homologous to the buccal cones of Clione. Nor have 



