Prof. W. Thomson on the " Vitreous " Spon(/es. 131 



The only known specimens of Hahrodictyon corhicula are in 

 the Museum of the Jardin des Plantes. They are three in 

 number : one is perfect, another is torn through the middle, 

 and the third is a mere fragment. Through the friendly cour- 

 tesy of M. Lacaze-Duthiers, I had an opportunity of examining 

 them carefully ; and, by his permission, an admirable photo- 

 graph of the perfect specimen was taken for me by M. Potteau. 

 This photograph is copied, reduced one-third in size, in PI. IV. 

 fig. 1. The specimen is labelled '■^ Alcyoncellum corbicula,Y 3i\. 

 Donn^ par M. Sadies. 1857." 



H. speciosu)7i, Quoy & Gaimard (sp.). PI. IV. fig. 2. 



Alcymicelliim speciosum, Quoy & Gaimard, ' Voyage de I'Astrolabe', Zoologie, 



vol. iv. p. 302. 

 Alcyoncellum speciosum^ Milne-Edwards, in Lamarck's 'Animaux sans 



Vertebres, vol. ii. p. 589. 

 Alcyonellum gelatinosum and A. speciosum, Owen, Trans. Zool. Soc. vol. ii. 



p. 205. 

 Alcyoncellum corhicula, Bowerbank, British Spongiadee, vol. i. p. 174. 

 Euplectella speciosa, Gray, Ann. & Mag. Nat. Hist. ser. 3. vol. xviii. p. 467. 

 Corbiiella speciosa, Gray, Proc. Zool. Soc. for 1867, p. 530. 



The Sponge is tubular, about 7| inches in height, exj)and- 

 ing gradually upwards from a contracted base 1^ inch in dia- 

 meter to a width of about 2^ inches at the upper extremity. 

 The network forming the wall of the tube is the same in ge- 

 neral structure and arrangement as in II. corhicula, but the 

 fibres are finer and more defined and compact in texture. The 

 wall of the tube rises to no definite lip, and forms no terminal 

 lid, but the ordinary network of the wall simply arches over 

 and closes the wide end of the tube without any change of 

 structure. As a rule, the spicules of the skeleton are identical 

 in form and arrangement with those of H. corhicula ; the fusi- 

 form spicules seem to be somewhat longer, and the irregular 

 hexradiate spicules less abundant. All the sarcode-spicules of 

 H. corhicula are repeated in H. speciosum in nearly the same 

 numerical proportions ; but in the latter species a minute spi- 

 cule (PL IV. fig. 2 a, X 1000) occurs in great abundance, while 

 it is rare, if it occur at all, in H. corhicula. This is probably 

 Bowerbank's "bifurcate rectangulated hexradiate spicule" 

 (British Sponges, fig. 188) ; it recalls in general character and 

 physiognomy a small spicule very abundant in the sarcode oi 

 Hyalonema, figm'cd in the ' Intellectual Observer ' of March 

 last, plate 1. fig. 10. The abundance of this special spicule in 

 H. speciosum has chiefly weighed with me in regarding the 

 two forms of Hahrodictyon as distinct species ; it would be ne- 

 cessary, however, to examine a larger series to arrive at a de- 

 finite conclusion on this point. 



