302 RHODALIIDAE. 



usually appears in works on invertebrate zoology, even in such an excellent work 

 as the "Traite" of Delage and Herouard, as a very remarkable group, although 

 but shortly after it was instituted Claus and Chun adduced conclusive reasons 

 for abandoning it. 



Apart from Angela, which must be removed from this family, the following 

 genera, all monotypic, no doubt belong here: — Angelopsis Fewkes ('86), Ste- 

 phalia Haeckel ('88b), Stephonalia Haeckel ('88b), Auralia Haeckel ('88b), 

 Rhodalia Haeckel ('88b), and Archangelopsis Lens and Van Riemsdijk (:08). 

 All of these have been described from more or less fragmentary specimens, but 

 it is certain that not all are distinct. Haeckel himself suggested the probability 

 that his Auralia might be identical with the Angelopsis of Fewkes, and Claus 

 ('89) has united Stephonalia with Stephalia, the former being merely a more 

 advanced stage of the latter. Both these reductions are accepted by Chun 

 ('97b, p. 104) and are no doubt justified. In examining the four remaining 

 genera we must bear in mind that none of the descriptions are satisfactory except 

 in some respects that of Ai'changelopsis. Thus Fewkes's account was taken from 

 very fragmentary material, while Haeckel's descriptions are not only based on 

 poor material but his figures are so largely reconstructed that it is difficult to 

 estimate them fairly. And even though the account and figures given by Lens 

 and Van Riemsdijk (:08) of Aixhangelopsis are based on serial sections, their 

 specimens were also so fragmentary that completeness was out of the question. 



With the foregoing caution in mind, three of the older genera can claim to 

 be distinct, notwithstanding the opinion of Schneider ('98) who united them 

 all under Angela. According to Haeckel ('88) Stephalia (Stephonalia) is dis- 

 tinguished by the presence of a permanent axial canal passing through the 

 centre of the bulbous trunk and connected with the primary siphon, as well as 

 by the absence of tentilla. Li Rhodalia and in Angelopsis (Auralia), on the 

 other hand, the canal system of the corm forms an irregular network, and tentilla 

 are present. The difference was made by Haeckel the basis for two families, 

 Stephaliidae and Rhodaliidae, but it is certainly of not more than generic import- 

 ance. I may also point out that inasmuch as no one, since Haeckel, has studied 

 Stephalia, it is impossible to determine how far his account of it is correct. 



Angelopsis is distinguished from Rhodalia by the presence of a very large 

 hypocystic cavity, a feature of importance (p. 309), and likewise by the presence 

 of a single row of nectophores (Angelopsis) contrasted with several rows (Rho- 

 dalia). I may point out however that the nectophores of the "Challenger" 

 specimens of Rhodalia were all detached (Haeckel, '88b, p. 303) ; therefore it is 



