128 Mr. H. J. Carter oji two Hexactinellid Sponges. 



fig. 1), Dr. Bowerbank figures faithfully a fragment of the 

 latter, which he finds not to be Myliusia callocyathes, but, al- 

 though very like in outward appearance to it, totally different 

 in structure ; hence he calls it " Myliusia Grayiy 



Having subsequently had to examine this sponge for the 

 late Dr. Gray, I saw that its minute structure (fig. 10) was 

 like that of the fossil species figured by Schmidt (Atlantisch. 

 Spongienf. Taf. ii..fig. 16) under the general appellation of 

 fossil spicules from " Scyph'a and Ventriculites " (Ann. & 

 Mag. Nat. Hist. 1873, vol xii. p. 365). Next I identified the 

 lantern-like knot of Myliusia Grayi with Mr. W. J. Sollas's 

 figures of the structure of the Ventriculites (Proc. Geol. Soc. 

 Lond. 1872, p. 65, fig. 2) ; lastly, Avith the late Mr. J. 

 Toulmin Smith's representations of the structure of the " Ven- 

 triculidie of the Chalk " (Ann. & Mag. Nat. Hist. 1847, vol. 

 XX. pi. vii. figs. 8-14. 



I next observed the lantern-like knot among the " Cretaceous 

 Microzoa of the North of Ireland," figured by Mr. J. Wright 

 (Report of Belfast Naturalists' Field-Club, 1873-74, Append, 

 iii., published 1875, pi. iii. fig. 7). After this I found it 

 myself among fossil sponge-spicules from the Mid Eocene of 

 Brussels, kindly sent me by M. Ernest Vanden Broeck. And 

 it again appears under another form in the beautiful illustra- 

 tions of the stiaicture of Cceloptychium agaricoides by Prof. 

 Karl Zittel of Munich (^Tleber Coeloptychium,' Miinchen, 1876, 

 Taf. iii. figs. 7-12). Finally in 1876 I obtained a slice of a 

 Ventriculite from Mr. Ed. Charlesworth, of the Strand, Lon- 

 don, and identified it therein myself. 



It was then that I saw the desi]-ability of illustrating the 

 only known living specimen of the kind, viz. Mylitisia Grayi 

 in the British Museum ; and having obtained permission of 

 Dr. Giinther for this purpose, I have done my best to publish 

 it ; for the specimen is very small, and, from its insignificant 

 appearance and dirty colour, would be very likely to be lost 

 sight of altogether, since it does not present the attractive 

 bright glassy aspect and sarcodeless character usually possessed 

 by the vitreous sponges after they have passed through the 

 the hands of the dealer. 



Although J/?/ ZiMsm C^ra?// presents the convoluted cerehriform 

 appearance of J/, callocyathes, yet its minute structure is to- 

 tally different, inasmuch as the knots or junctions of the fibre 

 in the latter are solid and round, not hollow and lantern-shaped 

 as in M. Grayi. Again, the general structure of M. Grayi , 

 although convoluted, is massive and labyrinthic throughout, 

 not cup-shaped or hollow in the axis as that of the Ventriculites; 

 while Cceloptychinm consists of radiating tubes more or less 



