In this pelagic province 26 species of Thecosomata have been found until now, which 

 are all mentioned in this Report; 23 of these species are represented in the collection, brought 

 home by the Siboga ; 4 of them are new. 



Of the 10 species of Gymnosomata, now recorded from the province in question, only 

 2 were not found again. Besides, 5 species out of the 8 had not been described yet. One 

 species belongs to a new genus. So, from a systematic point of view, we may say that these 

 results are satisfactory. 



Notwithstanding the anatomy of the two groups has already been studied by rather a 

 great number of previous authors, yet I thought it not superfluous to make another inquiry into 

 the anatom)-, to which I could perhaps contribute something and add a few corrections of former 

 statements. For anatomical purposes I made use of the material of the Siboga-Expedition, of 

 the Leyden Museum, of the Zoological Museum of Amsterdam and of the Utrecht Museum. 



It has never been my intention to give an anatomical monograph, nor even a complete 

 comparative study, as has already been so excellently done by Pelseneer ^). For such a 

 purpose, the material at my disposal has been insufficient. After the discussion of every genus, 

 I have given some anatomical notes, in which I confined myself chiefly to those facts, which 

 were new or contrary to previous assertions. 



Though I am aware of man)- lacunae in ni)- study on the anatomy, they are very often 

 not my fault, but due to want of material. For the rest, I greatly hope to complete these 

 researches and to add histological and embryological facts at the Naples Zoological Station. 



Lastly I have to thank my esteemed teacher, prof. Hubrecht, who, during my study 

 at the Utrecht Laboratory, assisted me with his great experience, also Dr. H. F. Nierstrasz, 

 who supplied me with material from Naples, and finally Dr. R. Horst, by whom the material 

 of the Leyden Museum was sent to me. Since my stay in London I keep in grateful 

 remembrance the names of Prof. F. J. Bell and mr. Edg. A. Smith, through whose kindness I 

 have had occasion to study the material of the Challenger, and the valuable collection of 

 thecosomatous shells in the British Museum. 



l) Challenger Report. LXVI. 



