ON THE NUDIBRANCHIATA. 17 



The rhinophores bear about fifteen perfoliations, which become less distinct at the top. 

 The dorsal margin makes five distinct undulations, so that the cerata appear to be set 

 in groups. But this is not really the case, the arrangement being as in N. gigas, 

 though perhaps the line of cerata is thinner and the bare space in the middle of the 

 back larger. There are a few large cerata inside the line. The longest measure 16 mm., 

 but most are short. 



The internal anatomy is as in N. gigas. It is hard to formulate any real difference 

 for the radula (18x4.1.4), but perhaps the denticulation of both the lateral and 

 rhachidian teeth is more distinct, and the innermost denticles of the latter are set 

 higher up on the side of the central cusp. 



1 am doubtful if this form should be regarded as a separate species, or merely a 

 variety of N. gigas, but its general appearance and colour are different ; it is much 

 smaller, though apparently sexually mature, and the oral tentacles are proportionately 

 longer. 



Tritoniadae. 



This family comprises the genera Tritonia and Marioma, the former without stomach 

 plates, the latter with them. To them, I think, should be added Atthila, which BERGH 

 makes the type of a separate family. It appears to me difficult to maintain the dis- 

 tinction between the genera Tritonia, Cuv., and Candiella, Gray. According to BERGH, 

 the " margo veli frontalis " is in the former " papilligerus " and in the latter " digitatus " : 

 the former has many and the latter few lateral teeth. Yet Tritonia exsulans, Bergh, 

 has 8-9 " einfache Finger" on each side of the frontal veil and a radula with a formula 

 of about 41 x 61.1.1.1.61, whereas -Candidla ingoljiana, Bergh, has "six fingers" on 

 each side of the veil and a radula of 67 x 83.1.1.1.83. I am, however, inclined to add to 

 the family two new genera, Tritoniopsis and Tritoniella. The former, described below, 

 has a divergent radula. Tritoniella, which I propose to describe among the nudi- 

 branchs found by the Discovery, resembles Tritonia in most points, but has dorsal 

 ridges, and instead of ramose branchise, simple projections or crenulations. Some of the 

 specimens are exceptionally well preserved, and it seems clear that no appendages are lost. 



BERGH'S list of Tritonia and Candiella in the System der Nudibranchiaten 

 poden contains sixteen species, to which the following have since been added : 



17. T. diomedea, Bergh. 



18. T. exsulans, Bergh. 



19. T. incerta, Bergh. 



20. T. giyantea, Bergh. 



21. T. (candiella,) australis, Bergh. 



22. T. (candiella) inyolfiana, Bergh. 



23. T, (candiella) villafranca, Vayssiere. 



24. T. appendiculata, sp. nov. 

 (ROY. soo. EDIN. TRANS., VOL. xu., 525.) 



