106 
THE VOYAGE OF H.M.S. CHALLENGER. 
The expedition has thus collected about 75 per cent, of known species, and if in 
this group it has only discovered a single new species, it has furnished numerous 
particulars relating to the geographical distribution both at the surface and in the 
deposits of the deep sea. 
From a systematic point of view the most complete results are those which refer 
to the fa mil y Limacinidse, the species of which are now clearly defined. The genus 
Peraclis, hitherto mistaken, has been studied and definitely re-established, an important 
fact in view of the light which the knowledge of this genus sheds on the relations 
of the Thecosomata to one another and to other Molluscs. In short, the classification 
of the family Cymbuliidse has been defined as far as is meanwhile possible. 
The anatomical results of the study of the Thecosomata are as important as those 
which were obtained from the study of the Gymnosomata, and, along with the latter, 
render it possible to determine the real affinities of the Pteropods, as will be shown in 
the third part of this Eeport. 
