44 



i88o. Hyalaea imitans Pfefier, Die Pteropoden des Hamburger Museums, Abh. Naturw. Ver. 



Hamburg, Bd. VII, p. 90, pi. VII, fig. <^a. 

 1884. Cleodora inflexa Sovvcrby, Thes. Conch., vol. V, Ptcropoda, pi. I, figs. 21 — 22. 

 1884. Diacria labiata Sowerby, Ibid., figs. 23 — 24. 

 1886. Cavolinia inflexa Locard, Prodrome de Conchyliologie frangaise, p. 22. 



Living animals: 



Stat. 36. 7° 38' S., 117° 31' E. I spec. 



Stat. no. 4° 34' N., 122° o' E. i spec. 



Stat. 12S. 4° 27' N., 1 25° 25'. 7 E. I spec. 



Stat. 148. 0° I7'.6 S., 129° 14'. 5 E. I spec. 



Empty shells: 



Stat. 88. o°34'.6N., 119° 8'.5 E. i spec. 



Stat. 223. 5°44'.7 S., 126° 27'. 3 E. i spec. 



Thi.s species is not nearly so abundant as the foregoing one. 



Hyalaea lAbiata d'Orbigny, regarded b)- the author, and man)- others after him, as a 

 distinct species, is only a variety of the type. Boas') described two varieties-, one of them, 

 longa, corresponds with Hyalaea mjiexa (in the sense in which -Souleyet -) uses the term), 

 while the other variet\- is designated under the name of lata (Hyalaea labiata Souleyet "). But 

 as in so many cases, these varieties are linked together (PI. II, figs. 54 — 63). 



The few specimens, brought home by the Siboga Expedition must be referred to the 

 form lata, which lives in the South-Atlantic, Indian and West-Pacific Ocean (Boas). 



Appendi.x to the Cavoliniidae. 



Several zoologists have described new "species" which in reality represent only young 

 stages of species, already known. Souleyet and Pfeffer have expressed in some cases, though 

 hesitatingly, their doubt as to the .specific distinctness of these small forms, referred to above ; 

 but it has been Pelseneer *) again who clearly pointed out their sexual immaturity. 



But thoug-h it is certain, that those forms with their extremely flat shells, without 

 completely developed closing apparatus, cannot be regarded as distinct species, it is almost 

 impossible to decide, to what species they must be referred. The characters of the adult forms 

 are only very vaguely expressed in the young ones, while (jn the other hand the embryonic shell 

 of the latter is always wanting in adult specimens of some species. These circumstances prevent 

 an exact solution of the question, which is not rendered more easy by the fact that several 

 young stages have been described or figured in a way so incomplete, that I think it will be 

 impossible to recognize the types, when occasionally found again. 



Anatomical investigations (in the case of Cleodora pygiiiaea and Pleitroptis longifilis) 

 have shown me, that the gonad does not exhibit lamellar structure, as in the adult, but consists 

 of numerous rounded follicles, just as in Clio (Creseis). Those of larger size are eggs, while 



i) Spolia atlantica, p. 123. 



2) Souleyet, Voyage de la Bonite, vol. II, p. 156, pi. V, figs. 21 — 26. 



3) Op. s. c. p. 159, pi. V, figs. 27—32. 



4) Chall. Rep. LXV, p. 71. 



