ADDITIONS. 



ISODTGTY'A DENSA, Plate L. 



Among tlie sponges sent to me for examination from 

 tlie Liverpool Museum, there was a box containing 

 numerous fragments of tliis species. They were in an 

 excellent state of preservation, and in eveiy chai-actor 

 were in perfect imison with the type-specimens from 

 Polperro by Mr. JSTormau. 



IsoDiCTYA Hyndmani, Boiverdanh. 



IlallrJiondria Ilijndmanh, Plate XL VI. 



From the very thin deposit of this sponge on the 

 shells of Pecten operculari^, on which it is usually found, 

 and from the complicated nature of its growth, it is 

 very often diffcult to determine the genus, as unless 

 the specimen of an Isodictya be viewed in a section at 

 right angles to its surface, it is very apt to be mis- 

 taken for a Halichondria, and this has been my case in 

 describing this species, in the first instance, from the 

 limited number of specimens in my possession. In 

 re-examining a considerable number of fresh ones in a 

 much finer condition than those on which I founded the 

 species, HaUcJtondria Hyndmani, I have been irresist- 

 ibly led to the conclusion that the species is truly an 

 Isodictya. A certain amount of alteration in the 

 sjoecific description will, therefore, be necessary, and I 

 propose that the following should be substituted for 

 the original one, page 2G4, Vol II. 



Isodictya E[yndmani, Bowerhanh 



Sponge. — Thinly coating or branching, and an- 

 astomosing ; branches issuing from small attenuated 

 bases, slightly compressed, terminations corymbose. 



