REPORT ON THE HEXACTINELLIDA. 101 



and while Bowerbank included in his genus Alcyoncellum, in addition to the well-known 

 species Alcyoncellum aspergilliim, the two species designated Alcyoncellum corhicula 

 and Alcyoncellum rohustum, Gray separated the genus Alcyoncellum from Euplectella, 

 and divided it into two genera, Corhitella and Heterotella. 



Corhitella, which included the single species (figured) Corhitella speciosa, was 

 characterised thus : — " The tube clavate, rather irregular, rounded at the end, formed of 

 slender fascicules of open elongate filiform spicules, placed in longitudinal transverse and 

 oblique directions, forming an irregular network ; " the genus Heterotella, on the other 

 hand, with the single species Heterotella corhicula, is defined as follows : — " The tube 

 short, rather irregular, conical, truncated, irregularly netted. Skeleton formed of thick 

 bundles of very numerous slender spicules, placed in all directions, and forming an 

 irregular network, similar to the network of the lid of Euplectella." 



Soon after this, however, AVyville Thomson, in his renowned contribution On the 

 Vitreous Sponges,^ again united the two genera of Gray, Corhitella and Heterotella, into 

 one, on account of the great similarity of their form, structure, and siliceous spicules, and 

 named the genus Hahrodictyon. His characters for this new genus are as follows :' — 

 " Sponge body subcylindrical, tubular, attached by a slightly contracted base. The 

 walls of the tube composed of a perfectly irregular network of bundles of siliceous needles 

 loosely and irregularly arranged in sheaves crossing one another at low angles, and 

 connected by a small quantity of soft mucilaginous sarcode. The spicules of the skeleton 

 all essentially of the hexradiate form, free and separate from one another, or rarely 

 connected in groups of two or three. The spicules of the sarcode numerous ' floricomo- 

 hexradiate stellate,' and various simple and branched modifications of the hexradiate 

 type." The two forms Hahrodictyon speciosuni and Hahrodictyon corhicida were 

 examined afresh in respect at least to the skeletons which had already been studied by 

 Bowerbank and Gray, and which are preserved in the Museum of the Jardin des 

 Plantes in Paris. One of these which bears the museum label "Alcyoncellum 

 coriicrJa, Valeneienne, donne par M. Saches 1857," and which was u?im.edi Heterotella 

 corhicula by Gray, exhibits a beaker-like inferiorly anchored tube, 10 cm. in 

 height and 5 cm. broad in the superior part, while its terminal opening is closed by a 

 transverse sieve-plate. The lateral wall of the tube consists of a very irregular 

 network in which the beams form irregular, roundish meshes, and are composed of loosely 

 united rod -like spicules varying in length up to 15 mm. No definite arrangement of 

 the beams of the network in transverse and longitudinal bands is exhibited, nor is there 

 any indication of externally projecting ridges. 



While the long rod-like spicules, which are somewhat thickened and rough at both 

 ends, merely exhibit in the middle four cruciately disposed lateral tubercles, as indications 

 of the six-rayed type, numerous well-developed six-rayed sj^icules also occur, which are, 



1 Ann. and Mag. Nat. Hist, ser. 4, vol. i. p. 114, 1868. * Loc. dt, p. 126. 



