358 SIR C. ELIOT OX XLTIBRAXCHS [DcC. 1, 



it does not seem possible to make any classification according to 

 this shape, and to unite, for instance, all the stellate forms. 



In most of the Cryptobi'ancliiata the tentacles appear to be 

 digitate, but the Archidorididte have a tendency (not without 

 exceptions) towards a flattened and furi'owed form. Sphcerodoris 

 has no tentacles, and the same is said of Holla and Echinodoris. 

 No part of presei-ved jSTudibi'anchs is more liable to distortion 

 than the tentacles, which may be vaiiously contracted, flattened, 

 or crumpled by the action of the preserving fluid or the pressure 

 of the adjacent parts. 



(c) The foot appears to off"er good characters ; as a rule, but 

 not invariably, the forms which have a broad foot and narrow or 

 mo lerate mantle - margin belong in other I'espects to groups 

 difl'erent from those which have a narrow foot overhung on every 

 side by a wide mantle -margin. The Archidorididfe and Disco- 

 dorididge have both, as a rale, broad feet, but the body of the 

 former is plump, and of the latter flattened. The Platydorididse 

 have flat bodies and narrow feet. 



In most forms the anterior margin of the foot is deeply grooved, 

 and the upper lamina notched so as to form two flaps, which in 

 the Kentrodorididfe are very ample. Many (though not all) of 

 the Archidorididpe have the anterior margin simply grooved and 

 otherwise entire. In a few ge\\QYa.{Trippa, Ualla*, tSphcerodoris) 

 the divided upper lamina is attached to the sides of the head, but 

 it does not seem possible to bring together the forms which 

 present this peculiarity. 



(d) In the internal anatomy, the mouth-parts are perhaps the 

 most im230rtant for classification. It is clear that considerable 

 strvictm-al differences in other organs are geneially accompanied 

 by a difierence in the radula. For instance, Acanthodoris and 

 Lamellidoris, which bear a strong supeificial resemblance to the 

 Cryptobranchiata but have no permanent gill-pocket, have also a 

 totally diftereut radula, and most of the larger divisions of the 

 Nudibranchiata have a characteristic ari-angement of teeth. But 

 it is hazardous to conclude from this that small differences of the 

 radula have a generic value. One common variation from the 

 ordinary hamate type of radula is the serrulation of the outer 

 teeth. This may be present or absent in the same genus (e. g. 

 Staurodoris verrucosa and St. bicolor), and in some species {Platy- 

 doris argo and Halgerda formosa f) is only found in some of the 

 rows of teeth. As a genei-al rule the innermost and outermost 

 teeth are smaller : the latter often rudimentary or degraded. 

 But it appears that these characters are only of specific, not of 

 generic importance. 



* [I venture to point out that the generic name Halla is preoccupied by a Poly- 

 chaste (Lumbricoiiereid) worm named i)y A. Costa in 1844 {cf. Ann. Acad. d. Aspiranti 

 Naturalist! Napoli, ii. p. 63 (1844). — C. Ceossland. 



t In a specimen oi' Hal jer da formosa from the Berlin Museum, given me by the 

 courtesy of' Prof. Martens, I found at the end of some but not all of the rows small 

 rudimentary teeth, some but not all of which bore a few irregular serrulatiotis. This 

 is not quite the same arrangement as observed by Piof. llcrgh. 



[6J 



