48 THE VOYAGE OF H.M.S. CHALLENGER. 



of the same length ; the hook-sacs, the radula, the buccal cones, the foot, &c, are quite 

 similar. In the living animal a red line exists on the fins, which, however, is not now 

 visible in the alcoholic specimens; but in other respects Clione elegantissima is exactly 

 the same as the young of Clione limacina. 



With respect to Clione dalli, Krause, this author says that it only differs from Clione 

 elegantissima by having two ciliated rings. The collected specimens measured from 

 5 to 6 mm., and had the radula similar to that in specimens of Clione limacina of the 

 same size. They are thus really the young of this species. 



2. Clione longicaudata (Souleyet). 



1840. Spongiobranchea elongata, d'Orbigny, Voyage dans rAmeiiqiie nieridioDale, t. v. p. 132, 



pi. ix. figs. 8, 9. 

 1850. Clione caudata, Gray, Catalogue of the Mollusca in the Collection of the British Museum, 



pt. ii., Pteropoda, p. 37. 

 1852. Clio longicaudatus, Souleyet, Voyage de la Bonite, Zoologie, t. ii. p. 28G, pi. xiv. 



figs. 17-21. 



Body very long, with posterior part very pointed. 



Foot. — Anterolateral lobes large, wide in front, pointed posteriorly ; posterior lobe 

 probably very short ;* Souleyet says 2 that the foot of Clio longicaudatus is like that of 

 Pneumonoderma, without the posterior lobe. But the anterior lobes being very large, 

 they probably hid the posterior lobe, as often happens in Clione limacina. Besides, 

 we have seen that, in this last species, there are some specimens with the posterior lobe 

 of the foot very small ; but however minute it may be, this lobe is always distinct, and 

 exists in all the Clione {Clione limacina, Clione jlavescens) and in all the other Gymno- 

 somata, except Clionopsis. It is therefore very improbable (as Ihering 3 following 

 Souleyet 's figure states) that Clione longicaudata has no posterior lobe to the foot. 



Proboscis rather short. 



Buccal Appendages. — Two pairs of cones, like those of Clione limacina. 



Colour. — Dark brown. 



Length. — Does not measure 10 mm. (Souleyet). 



Habitat. — Atlantic Ocean, lat. 10° N., long. 21° W.; " Spongiobranchea elongata," 

 which I identify with the present species, was gathered in lat. 4° N., long. 25° W. 



Observation. — " Spongiobranchea elongata," d'Orbigny, is in reality not a Spongio- 

 brancheea; in the shape of the body, head, and foot, it quite resembles Clione longi- 

 caudata. The habitats of the two forms make their identity still more certain, the 

 localities where they were gathered being very close to one another. 



1 The type-specimen of Souleyet, in the Museum of Paris, being quite destroyed, and d'Orhigny's specimens not 

 having been preserved, it was impossible to definitively decide on this point until new specimens had been obtained. 



2 Voyage de la Bonite, Zoologie, t. ii. p. 286. 



3 Vergleichende Anatomie des Nervensystem und Phylogenie der Mollusken, p. 248. 



