358 SIR c. ELIOT OX xuDIBKA^-cns [Dec. 1, 



it does not seem possible to make any classification according to 

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



In most of the Cryptobranchiata the tentacles appear to be 

 digitate, but the Archidorididfe have a tendency (not without 

 exceptions) towards a flattened and furrowed form. Sphcerodcn'is 

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

 No part of preserved Nudibranchs is moi'e liable to distortion 

 than the tentacles, which may be vaiiously conti-acted, flattened, 

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

 of the adjacent parts. 



(c) The foot appears to offer good characters ; as a rule, but 

 not invariably, the forms which have a bi'oad foot and nairow or 

 moderate mantle - margin belong in other respects to groups 

 different from those which have a narrow foot ovei'hung on every 

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

 dorididse have both, as a rule, broad feet, but the body of the 

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

 have flat bodies and narrow feet. 



In most forms the antei'ior margin of the foot is deeply grooved, 

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

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

 the Archidoi'ididye have the anterior margin simply grooved and 

 otherwise entire. In a few geneva, {Ti-ippa, Halla*, Sphcerodoris) 

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

 it does not seem possible to bi'ing together the forms which 

 present this peculiarity. 



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

 most impoi'tant foi- classification. It is clear that considerable 

 structui'al difl:erences in other organs are generally accompanied 

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

 Lamellidoris, which bear a strong superficial resemblance to the 

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

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

 Nudibranchiata have a characteristic arrangement of teeth. But 

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

 radula have a geneiic 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. 

 Staurodo7'is verrucosa and St. bicolor), and in some species {Platy- 

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

 rows of teeth. As a general I'ule the innermost and outermost 

 teeth are smaller : the latter often rudimentary or degraded. 

 But it appears that these cliaractei's are only of specific, not of 

 generic importance. 



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

 chsete (Lumbriconereid) worm named by A. Costa in 1844 (<•/. Ann. Acad. d. Aspiranti 

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



t In a specimen oi Halgerda 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 

 nidnnentary teeth, some but not all of which bore a few irroja-ular serruhitions. This 

 IS ijot quite the sauie ia-ranyemcut as obser\-cd b^- I'ruf. Bcru-li. 



