716 PROF. A. BENDY AND MR. R. W. H. ROAV ON 



1883. It appears to us that the time has come, owing to our 

 greatly increased knowledge of the group, to abandon this primary 

 division, and we now propose to consider the class as consisting 

 of a single order only. 



One reason for taking this step lies in the discovery of various 

 intermediate forms. Such are the species of Deoidya, which in 

 the radial arrangement of the ascou tubes approach closely to the 

 Leucascid type of Heteroccela, and the species of Leucascus itself, 

 which are but slightly modified from homocoel ancestors and 

 form the starting-point of a distinct evolutionary series within 

 the group Heteroccela ; while von Lendenfeld's Homoderma 

 sycandra is obviously merely a Sycon in which the collared cells 

 persist in the central gastral cavity throughout the life of the 

 sponge. 



Another even more important reason lies in the fact that, as 

 noted above, the group Heteroccela is at least diphyletic in 

 origin, the genus Dendya and the family Sycettidte forming two 

 distinct starting points from which the evolution of the higher 

 Leviconoid forms has proceeded. 



We therefore propose to divide the class Calcarea straightway 

 into families, of which the first will be the Homoccelidse, practi- 

 cally co-extensive with the Homoccela of Polejaeff. His group 

 Heteroccela, on the other hand, is here definitely abandoned, 

 being represented by the families Leucascidse, Leucaltidse, Min- 

 chinellidse, Murrayonidfe, Sycettidae, Heteropiidte, Grantiidse, 

 Amphoriscidse and Lelapiidse. 



Family 1 . HOMOCCELID^ nov. 



Diagnosis. The whole of the gastral cavity and its various out- 

 growths lined by collared cells throughout the life of the 

 sponge. Sponge colony rarely radiate, and, if so, the central 

 individual retains the primitive ascon structure, with a 

 lining of collared cells and without a special gastral cortex. 

 No true dermal membrane or true dermal cortex is ever 

 developed. 



In 1872 Haeckel proposed seven genera of " Ascon" Calcarea, 

 based upon the permutations and combinations of triradiate, 

 quadriradiate, and oxeote spicules. This constituted his so-called 

 " natural " system, but he also had an " artificial" system based 

 upon the type of colony formation. Both systems have shown 

 themselves far from satisfactory in practice and have long since 

 been abandoned. 



In 1883 Pol6jaefl", recognising the extreme difficulty of sub- 

 dividing the group, placed the whole of the species in the genus 

 Leucosolenia of Bowerbank, which takes priority over all Haeckel's 

 genera and is the only genus recognised by Polejaeff" in his order 

 Homoccela. 



