180 Mr. H. J. Carter on new Species of Subspherous Sponges . 
is evidently a variety of Geodia arabica (Annals, 1869, vol. ii. 
l. c.), differing only in the canal-system being less arborescent 
and the ends of both the shafts and branches of the large tri- 
radiate spicules of the circumference being frequently obtuse, 
rounded, or inflated—thus more resembling Pachymatisma. 
But the body-spicule of Pachymatisma, being round or in- 
flated at both ends, alone distinctly separates it from Geodia ; 
while Tethya lyncurium, from the absence of the furcate spi- 
cules, on the one hand, and the position of the large stellate 
spicules (which are for the most part situated on the inner side 
of its cartilage-like crust), on the other, is neither a Tethya 
nor a Geodia, nor a Pachymatisma (see my figures, * Annals,’ 
l.c.), Hence Tethya lyncurium should also have a separate 
nus. 
As regards the describing of sponges generally, it is very 
desirable that no spicule should be figured in connexion with 
them which is not strictly characteristic of the species. The 
introduction of varieties and monstrosities, with which every 
specimen more or less abounds, I am persuaded is as much a 
mistake as it would be to omit them from a dissertation de- 
voted to the formation and development of the spicule gene- 
rally. Here the varieties and monstrosities might appear to 
advantage; but figured with the characteristic spicules of the 
species in which they may have been observed, they are only 
calculated to confuse and mislead. 
have therefore, although I have found different hamate 
and stellate spicules about the specimen of Tethya atro-purpurea 
(above described), regarded them as adventitious products, 
which it is more desirable to retain mounted in balsam for the 
and, growing there, had thus become incorporated, and had 
produced the group of triradiate spicules to which I have 
alluded. 
