REPOET ON THE H EX A CTLN'ELLIDA. 103 



Other respect closely related to Hahrodictyum corhicula, as a quite distinct and separate 

 genus from the latter, and further, the fact that in Hahrodictyum speciosum no terminal 

 sieve-plute is present, led Wyville Thomson to object to the opinion which had been 

 expressed by Boxverbank,' to the effect that in Euphctella and allied sponges " the 

 openings of the Ud and those of the tube stand to one another in the relation of oscula 

 and pores." He maintains that on the contrary " each of the large openings of the wall 

 is occupied by an exhalent orifice and that inhalation takes place as usual by minute 

 pores in the interstices between the spicules of the skeleton." 



Carter says in his treatise On flexactinellidse, ■ " Alcyonellum speciosum and 

 Alcyonellum corhicula appear to me to belong to one and the same species," which 

 opinion I assent to. 



The genus Hahrodictyum probably also includes Eudictyiim elegans, Marshall, which 

 Marshall has briefly described from a hoUow, canal-like form (presers'ed in the Museum of 

 the Amsterdam Zoological Garden), agreeing with Hahrodictyum speciosum, Quoy and 

 Gaimard, in the form and structure of its irregular, lattice-like skeleton, though 

 exhibiting in the interior a looser spicular work (of interstitial connective tissue — 

 Flockengewebe). The latter consists, according to Marshall, chiefly of long (up to 1 cm.) 

 rod-like spicules, between which slender, sword-shaped hexradiate forms occur, besides 

 more delicate six-rayed and five-rayed spicules, with irregulai'ly developed prickles, 

 and further, small crowded forms, with six, five, four or three rays, which, like the two- 

 rayed so-called compass spicules, probably form wreaths round the dermal ostia. 

 Particularly characteristic are the six-rayed spicides, 0'2 to 0"3 mm. in axial length, 

 which bear on the extremity of each ray a disc with seven prongs. Marshall's bristle- 

 like spicules also occur, as well as the well-known " floricomo-hexradiate rosettes," which 

 do not differ essentially fr-om those of Euplectdla. 



In the memoir which appeared iu 1876,^ Marshall characterised the family of the 

 Euplectellidse as follows : — " Pollakid Hexactiuellidse of tubular form, monozoic, osculum 

 closed by a sieve-plate; in the_ parietal tissue longitudinal, circular and spiral bundles. 

 Dermal skeleton chiefly formed of hexradiate spicules, between which lie the smaller dermal 

 pores. Large crateriform elevations of the parietal tissue also occur. There are also a con- 

 siderable number of dermal ostia which lead directly into the body ca^-ity, and which may 

 be closed by compass spicules. The rosettes belong to the ' floricomo-hexradiate ' type." 



In the genus Euphctella, Marshall notes two species, namely, Euplectella aspergillum, 

 Owen, and Euplectdla oweni, Marshall and Herklots, and in the genus Hahrodictyum, 

 Wyville Thomson, only the single species Hahrodictyum speciosum, Quoy and Gaimard, 

 leaving it imdecided whether the sponge {Eudictyum elegans) he had described, from the 

 Amsterdam Museum, is an independent form, or belongs to the Hahrodictyum speciosum. 



I British Spongiadfe, vol. i. pp. 176, 177. ^ Ann. and Mag. Nat. Hist., ser. 4, vol. rLL p 368. 



^ Ueber die Yerwandtschaftsverhaltnisse der Hexactinelliden, Zeitschr. f. iciss. ZooL, Bd. .\xvii. p. 128. 



