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



PTEROPODA. 



65 



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Microdonta nov. gen. 

 PI. IX. 



Radula with small and numerous teeth. Median 

 tooth sickle-shaped without denticles. (Textfig. 52). Lateral 

 teeth hook-shaped. 



Jaw: A median row of spines continued on each 

 side by a series of small single denticles. 



Hook-sacs shallow, with short, not very strong 

 hooks. A group of large clear cells on the dorsal side 

 of each hook-sac forms a cushion-like protrusion. 



Proboscis well developed, long and narrow, mouth 

 opening towards the dorsal side (fig. 69, 71). 



Posterior gill may be present. 



Foot without a median tubercle. 



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Fig. 57. Buccal organs of Fowlerina hjortii: 

 jaw; hook-sacs. 



Fig. 58. Spines of the jaw of Fowlerina hjortii. 



Hook-sacs with 13 og 14 short strong hooks. 

 Foot: Lateral lobes large, fixed anteriorly and later- 

 ally; posterior lobe short, pointed. 



Wings truncated with a narrow base. 

 Posterior gill consisting of a membranous ring 

 near the posterior end of the body. In front of this ring 

 the skin is longitudinally folded so as to give the body 

 a quadrangular cross-section. 



Skin transparent, unpigmented. 

 Size: 5—9 mm. in length. 



St. 10: 45° 26' N, 

 Date 19 A— - l U 1910. 

 St. 

 50, 



Localities: 



9° 20' W. Surface. 



1 individual. 

 92: 48°29'N, 13° 55' W. Depths: 

 150, 1000 m. Date 23 / 7 — 24 A 1910. 



5 individuals. 



Microdonta longicollis n. sp. 



PI. IX, fig. 69-78. 



In the external appearance this species stands midway 

 between Notobranchaea and Fowlerina. It has the spindle- 

 shaped body and the narrow neck of the former, while 

 the head and proboscis remind one of the latter, although 

 they are relatively smaller than in that form. 



The radula with its small and numerous teeth is in this 

 genus of a rather aberrant type, but still the median tooth 

 has kept the sickle-shape with the concave free margin, 

 characteristic of the whole family of Notobranchaeidae. 



Radula tongue-shaped with a longitudinal groove 

 along the median line. Formula 10—1 — 10. (Fig. 74, 78). 



Jaw: Median row of 8 or 9 double-pointed spines 

 (fig. 75 — 77), on each side 5 single denticles. 



Hook-sacs shallow, with about 17 hooks (fig. 72 — 

 74). The group of clear cells, present also in Noto- 

 branchaea and Fowlerina, forms in this species a large 

 and very conspicuous cushion dorsal to each hook-sac 

 (fig. 74). The meaning or these organs is not at all 

 clear, and I hope in a later paper to discuss their structure 

 and relations. 



Foot: Lateral lobes converging anteriorly; posterior 

 lobe narrow and pointed (fig. 70 — 71). 



Wings narrow at the base and tapering towards 

 the distal end. 



Posterior gill formed by four radiating crests 

 meeting at the pointed posterior end of the body (fig. 

 69, 70). 



Skin smooth, unpigmented. 



The largest specimen was 7 mm. in length, the length 

 of the proboscis being equal to two-thirds of the rest of 

 the body. 



Locality: St. 5 8: 37° 37' N„ 29° 25' W. Date: 

 "/«— 18 /e 1920. Depth: 50 metres. 



