SOLENOGASTRES. 9 



As a consequence of these facts, to which might be added many others concerning 

 the structure of the digestive tract, nervous system, etc., we must acknowledge that 

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

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

 between weberi and australis, for instance, is greater than that between weheri and 

 Rhopalomenia indica or Dinomenia. The same holds good for Rhopalomenia itself 

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

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

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

 papillae (13, p. 272). In this sense the genus Rhopalomenia 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 thulensis ; 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 gerlachei, 

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

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

 do not correspond in many respects. 



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

 neapolitana is a distinct form {Amphimenia of Thiele, 13, 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 spicules), 

 though in the latter form cloacal spicules are wanting. 



Indo-pacific forms : weheri, longa, amboinensis, australis, valdiviae and hawaiensis. 

 Of these forms hawaiensis is insufficiently known ; only the nervous system has been 

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

 amboinensis, however, must be considered an isolated form, on «iccount of the structure 

 of the radula and the coelomoducts. Australis has a biserial radula, valdiviae a 

 multiserial 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. 



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

 species of Pro7ieomenia present great differences ; all of them, however, have a radula, 

 a thick cuticle 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, however, we have good reason to divide the genus into a number of smaller 



VOL. IV. C 



