CXXll 
THE VOYAGE OF H.M.S. CHALLENGEE. 
is a combination that by the accepted laws of nomenclature cannot possibly be disturbed, 
since the species is the tjrpe of the genus so named by Lamarck, and accepted and 
redefined by 0. Schmidt in 1862. A new name should therefore have been found 
for Tethya cranium. Gray, however, unfortunately substituted Nardo’s name, Donatia 
aurantiaca, for Tethya. lyncurium, of which it is a mere synonym, and left Tethya 
cranium to stand. This proceeding has naturally led to some confusion, but the 
error was not long left uncorrected, 0. Schmidt,^ some three years later, proposing a 
new genus, Craniella, to receive Tethya cranium, and leaving Tethya lyncurium in 
enjoyment of its established rights. 0. Schmidt, however, included Craniella and its 
near allies, together with less closely connected Sponges, such as Stelletta, in his family 
Ancorinidse; and we owe to Carter ^ their separation as a distinct subfamily group. Carter, 
adopting Gray’s nomenclature for Craniella cranium^ named this group Tethyina, a 
term which it is impossible to retain. The Challenger material has added two new genera 
to the group, and it has become important enough to be raised to distinct family rank ; 
indeed, independently of these fresh accessions, its claim to be regarded as a distinct 
family would naturally be admitted on account of the sharp line of demarcation which 
exists between it and the other members of Schmidt’s Ancorinidae. Selecting Tetilla, 
the most primitive genus of the family, as the type, I propose for it the name Tetillidae. 
Definition. — The Tetillidse are Sigmatophora distinguished by characteristic pro- 
trisenes, which never fail, and by sigmaspires, which not unfrequently are absent. 
No other Sponge can well be mistaken for a Tetillid ; wide and numerous as are the 
variations which occur within the limits of the family, the facies remains the same ; it is 
not always easy to say on what particulars a facies depends ; in this case 1 think these 
will be found first in the form of the protrisene, which is not exactly repeated in any 
other group of Sponges ; next the anisoactinate character of the oxeas may have some- 
thing to do with it, for though such spicules occur in other Tetractinellids, I do not know 
of any in which they are present to the same extent ; finally the sigmaspires when present 
are highly characteristic. 
The Skeleton. — The different forms of megascleres met with in the family are — 
1. A somal oxea, which varies from 1‘27 to 8 mm. in length according to the species ; 
it is usually anisoactinate but sometimes isoactinate, the ecactine being shorter and 
more bluntly pointed than the esactine. 
2. A cortical oxea, which differs from the somal chiefly in being much smaller and 
usually isoactinate. 
3. Protrisenes, which may be isocladose, or anisocladose in the latter case two ; of the 
cladi are usually of equal size, and smaller than the third. These spicules, as also the 
oxeas, are frequently trichodal. 
^ 0. Schmidt., Spoijg. Atlant. Gebiet., p. 66, 1870. 
“ Carter, Ann. and Mag. Nat. Hist., ser. 4, vol. xvi. p. 67, 1875. 
