566 SIR CHARLES ELIOT. 



Gen. Pleuroleura Bgh.' {= Dermatobranchus van Hasselt). 



The genus Pleuroleura, which is practically Pleurophyllidia without gills or side lamellae, 

 is made by Prof. Bergh the type of a separate family. But as it differs from Pleuro- 

 phyllidia only in the point mentioned and agrees with it in numerous distinctive peculiarities, 

 it seems better to include both in one family, like Tetlnjs and Melibe, of which Tethi/s has 

 gills while Melibe has none'-. 



The history of the genus is somewhat remarkable. Van Hasselt described three species 

 of Dermatobranchus in 1824. In 1874 Bergh created the genus Pleuroleura for a fourth 

 species (ornata) and held that there was not sufficient evidence to identify it with Dermato- 

 branchus as van Hasselt's specimens were lost. He subsequently discovered them in the 

 Leyden Museum and in 1888 (I.e.) expressed the opinion that the identity was practically 

 certain, but maintained the name Pleuroleura all the same. By the rule of priority there 

 can be little doubt that the genus should be called Dermatobranchus, but that rule is not 

 an end in itself but a means to an end, namely to find one name for one genus or species. 

 When two names have approximately equal claims the earliest ought certainly to be taken. 

 But when hardly anything is known of the animal under the earlier name and practically 

 all our knowledge comes from descriptions published under the later name, it appears to 

 me that the principle at stake is not sufficiently important to outweigh the inconvenience 

 of resuscitating the original designation, a reference to which would give an enquirer very 

 little information. 



Pleuroleura strongly resembles Pleurophyllidia in appearance, but the known species 

 seem somewhat smaller and have no warts or papillae on the neck. The tentacular shield 

 is perhaps not always so distinct as in the other genus. The rhinophores are set close 

 together, but emerge from separate short sheaths and bear longitudinal folds. The sides of 

 the body bear no af)pendages, and there are no branchial clefts. The jaws, radula, digestive 

 and reproductive apparatus are all similar to those of Pleurophyllidia. The mantle margin 

 is perforated by cnidopores. 



Bergh gives as a family character of the Pleuroleuridae, Notaeum antice in nucham 

 tramiens. If I am right in supposing this to mean that the mantle margin is not con- 

 tinuous in front but interrupted and that the dorsal surface and neck are consequently 

 continuous^ the character is not possessed by the specimen here examined and apparently 

 not by Pleuroleura fortunata (Bergh, I.e. 1888, PL X. figs. 1 and 3). 



Pleuroleura is recorded hitherto only from the Philippines, the Malay Archipelago, East 

 Afi-ica, and Spitzbergen^ Nothing whatever is known of its habits. 



29. Pleuroleura striata (van Hasselt). 



Mr Gardiner furnished me with a single specimen fjund by the Skeat Expedition in 

 Pulau Bidang. It is externally well preserved but very hard and brittle. The form is rather 



' van Hasselt, Allg. Kmist en letterbode, 1824, 2. 3. 4. has no branchial clefts but side lamellae only. 

 Bergh, S. R. vt. p. 276 fl. 1874. Id. "Die Pleuroleuriden," ■■ This appears to be the case in Linguella, v. Bergh, 



Zool. JahrbiicJier : Ahth. fiir Systematik, 3 Baud, 3 Heft, Anatomisk Uiiderspgehe af Sancara quadrilateralis, Pla.te xiu. 



Jena, 1888. figs. 1 and 5. 



- I have since discovered in East Africa a form which I ■• Pleuroleura Walteri, Krause, " Moll, von Ost-Spitz- 



call Pleurophyllidiella and which seems to be a connecting bergen," in Zool. Jalir. Jena, 1892, p. 366. 

 link between Pleurophyllidia and Pleuroleura inasmuch as it 



