46 F. A. SMITT, 



primary aperture, most alike the Escharella auriculata, under the subgeneric name of 

 Herentia, I placed it at the side of that species, though expressly remarking x ) its signi- 

 ficance of a connecting link between the Escharellidan and Hippothoan types; but now, 

 through the southern forms, in seeing it still more nearly combined with the last- 

 named type, in its divergence towards the Celleporine constitution, most conveniently 

 it will be placed at the side of the preceding species. 



The typical Hippothoa linearis I have not found among the Pourtales collections, 

 but the variety of the same type, which, after Busk, I have identified with the tertiary 

 Eschara biaperta by Michelin, seems to be very common in the Floridan sea. 



Hippothoa biaperta*) (Pl. VIII, figs. 173 — 176). 



It was found by Pourtales growing on shells and corals, particularly small ones 

 of the Gorgonian tribe, in an encrusting state or raisecl in small but, relatively, broad 

 expansions of Escharan (auctt.) construction 3 ), in a varying depth of from 9 to 60 

 fathoms. 



With the greater richness of specimens, in different degrees of development, it 

 presents also a greater fullness of developmental changes, than what we knew before. 

 Sometimes, the young zooecia (fig. 175) are distinctively perforated, all över the front, 

 by pores, which never seem entirely to want, though, sometimes (fig. 173), they are 

 obscured, or rather less distinctively marked, in the lowest degrees of calcification. 

 Usually, they are greatest at the margins of the zooecia, where, in the older zooecia, 

 they are only persistent. The younger zooecia, when unworn, in the feebler calcifica- 

 tions at least, have their aperture, with a breadth of about 0,os — 0,oy mm., crowded by 

 6 or 7 bristles; and sometimes, in 1 or 2 pairs, on the older and thickened zooecia 

 also, these bristles will be found, even at the development of the ooecia. The form of 

 the avicularia, in the same manner as we have observed on northern specimens, is 

 varying, round or acute, the one or the other form, sometimes, in different colonies, 

 being more exclusively predominant; sometimes these two forms occur profuseky to- 

 gether. The ooecia, which, on the northern specimens, we did not know, have a roundec! 

 form. From their base they are covered by a thicker, annular layer, which, on their 

 front, leaves a semich-cular space of feebler thickening. This space, in the same man- 

 ner as the front of the zooecia, is more or less distinctively perforated by pores; in 

 the former case it is striated, in a radiating manner, by furrows converging from the 

 pores towards the middle of the apertural margin. 



The supernumerary avicularia, most commonly of the acute form, of this Hip- 

 pothoa, of course, are to be accounted for in the same manner as those of the typical 

 Hip>pothoa linearis and of the Hippothoa spongites. The occurrence, nuniber and size of 

 these defensive organs seem to belong upon special cases of need, afforded by outer 

 circumstances; but it is a general rule, that the more the Escharines approach to the 



') ÖlVers. Vet. Akad. Förh. 1867, p. 479. 



-) Synonyma vide in Öfvers. Vet. Akad. Förh. 1867, Bih., p. 14. 



'■'') Not unlike the fig. 193 (see below). 



