NUDIBRANCHIATA. 543 



retractile into sheaths. Branchiae consisting of arborescent tufts set in a single row along 

 the pallial margin. Buccal mass very large ; mandibles powerful. Radula wide, with a broad 

 central tooth, the first lateral larger than the rest. Liver not at all ramified. Vent lateral. 

 No blood-gland. One spermatotheca. Reproductive system unarmed. 



Setting aside the disputed genus Hancockia Gosse, the family may be considered to 

 comprise three genera, Tritonia Cuv., Marionia Vayssiere, and Atthila Bergh. Although the 

 creator of the last named considers it sufficiently distinct to form a new family, it has 

 clearly great affinities to Tritonia. The characters of the latter genus are as follows. The 

 frontal veil bears papillae and there are two spoon-shaped tentacles. The rhinophores are 

 not laminate but have a single club, surrounded by pinnate filaments. There are no dorsal 

 apjjendages except the branchiae and no stomach plates. Most authors recognize as a sub- 

 genus Candiella Gray {Figures of Moll. Animals, iv. 1850) distinguished by having only a 

 few digitate processes on the frontal veil and a somewhat narrower radula. The genus 

 Marionia Vayssiere resembles Tritonia externally, but the stomach is anned with a series 

 of homy plates. Generally but not always the appendages on the frontal veil are branched. 

 The genus Atthila, instituted by Bergh for a single specimen obtained by the Ingolf ex- 

 pedition in the northern Atlantic, has the frontal veil entire, and rhinophores of the 

 ordinary lamellate type. On the back are three rows of appendages, probably all simple, 

 but the specimen was somewhat damaged. In their general characters the branchiae and 

 buccal parts resemble Tritonia. 



The Tritoniadae are not numerous in collections, being inhabitants of faii-ly deep water 

 and only obtainable by dredging, but seem to be cosmopolitan in their distribution. They 

 are recorded from the Mediterranean, the Northern and Arctic Atlantic, Brazil, the Pacific 

 coast of Patagonia, California, the Arctic Pacific, Hawaii, the Cape, the Red Sea, and the 

 Malay Ai'chipelago. Marionia is recorded from a less wide range than Tritonia, but it is 

 probable that several species described under the name Tritonia should really be refeiTed 

 to the latter genus. 



The Tritoniadae are sluggish but voracious animals, living largely on Alcyonium, large 

 chunks of which are often found in their stomachs. The spawn is a simple string-like coil 

 deposited on seaweeds or corallines. 



The present collection contains only a single representative of the family belonging to 

 the genus Marionia, created by Vayssiere, and characterized by the presence of a girdle 

 of homy plates set round the stomach. 



Marionia Vayssiere'. 



1. Marionia arborescens B. (S. R. Heft xvii. pp. 890—894, PI. LXXXVIII). 



One specimen from Fadifolu Atoll, Maldives, 12 — 25 /. (fathoms). The species was 



established by Bergh for four specimens captured by Brock at Amboina. The specimen 



contained in the present collection agrees well with his description but is somewhat smaller, 

 being only 3'5 cm. long and 1'3 broad. 



' Vayssiere, " Sur un nonveau genre de la famille des Jourii. de Conchyl. 3. S. xix. 1879, pp. 106 — 118. Bergh, 

 Tritoniad^s," Comptes rendits de Vac. des sc. lxxt. 1877, "Beit. zueinerMonogr. der Gattung Marionia, V." Mittheil. 

 pp. 299—301. Id. "Description de la Marionia Berghii," aus der Zool. Stat, zu Neapel iv. 2. 1883, pp. 303—326. 



