9 



Aa a coi).T,|ii-nre of these facts, to which might } added many others concerning 

 the structure <>f the digestive tract, nervous system, etc., we must acknowledge that 

 there exist great differences lietween the various species of Proneomenia, and 

 consequently it would be rational not to class them in one genus. The difference 



L'tWeeil ' ; . :i!i.| //-'.;/-. !',,] m-r.ill. -. 1- _!., ;,T li.u, i],.,; !..:\\,.;i W|j .,!.,: 



Rhopalomenia indica or DJ/I.-//I. ////. The same holds good for Rliopalomenia itself. 

 This genus was created by Simroth on account of the presence of club-shaped 

 pi.lermal papillae (12, p. 229). It is with good reason that Thiele observes, that 

 the absence of a radula is more typical of Rhopalomenia than the presence of the said 

 jiapillar (13, p. 272). In this sense the genus Rhopalnrnenia was enlarged by me, 

 some years ago, to contain new species (6, p. 22). 



As to the geographical distribution, nothing confirmative is given. Arctic 

 are sluiteri and tliulrnsu ; both forms are most certainly not closely related 

 (14, p. 115). 



Antarctic forms : gerlachei and discoveryi. Between these two forms there exist 

 great differences (dimensions, radula, dorsal spicules, buccal gland of yrrltichei, 

 structure of the proximal portion of the digestive tract). In dimensions, gerlachsi 

 resembles sluiteri ; for the rest, according to Pelseneer (10, p. 34), these two forms 

 do not correspond in many respects. 



Mediterranean forms: neapolitana, gorganophila, desiderata, vagans. No doubt 

 neapolitana is a distinct form (Amphimenia of Thiele, 18, p. 244). Vagans, 

 desiderata and gorgonophila agree in the structure of the pharynx and salivary glands 

 (5, pp. 59, 76); the index, however, varies from 6 to 25. Yet I am inclined to 

 consider these forms related to each other. Vagans differs importantly from sluiteri, 

 gerlachei and discoveryi, by the structure of the radula ; on the other hand, a relation 

 with thulensis is very well possible (radula, salivary glands, abdominal spiculcs), 

 tin nigh in the latter form cloacal spicules are wanting. 



Indo-pacific forms : tceberi, longa, amlminenxis, australis, valdiviae and haicaiensi*. 

 Of these forms haicaiensis is insufficiently known ; only the nervous system has \>een 

 accurately studied by Heath (1). Weberi and longa, no doubt, are related ; 

 MH&0MMM^ however, must be considered an isolated form, on account of the structure 

 of the radula and the coelomoducte. Australit has a bisehal radula, valdiviae a 

 multiscrial one (9, pp. 681, 672). 



Atlantic forms: acuminata shows a multiserial radula and two salivary glands, 

 which open out separately. Abdominal and cloacal spicules are wanting. 



Recapitulating these facts, we come to the following conclusion. The known 



-;.. : - "'. /' ' ' i I.P-M L'l.Ml -liti". -r.-n.-.., ; .-ill .,(' t':..-ni. i,..\\. \.T. h.iv.- .1 IM-I ;!.,. 



a thick cutii-le with many layers of pointed, hollow spicules, numerous epidermal 

 sense-organs, and one or more dorso- terminal sense-organs ; gills are wanting. If no 

 other characteristics were considered, we might keep the genus Proneomenia. In my 



opinion, IIOW.-V.T. \w ha\r good reason t<> divide the L'fiiu-* into a nuniltrr of sinalli-r 



VOL. IT. C 



