REPORT ON THE HEXACTINELIJDA. 353 



description ran : — " Sponge, siliceous, funnel-shaped, fixed by the base ; the upper sur- 

 face smooth, marked with numerous minute perforations placed in nearly parallel 

 grooves, radiating from the centre to the circumference, and with numerous large, olilong, 

 rather unequal-sized perforations, which are fringed on the lower side with a high wall of 

 a similar structure to the rest of the sponge ; these edges of the cavities causing the 

 under surface to be covered with unequal irregular-shaped tubes of nearly the same 

 length, and more or less confluent together : some of these tubes are simple and sub- 

 cylindrical, others are expanded and more or less crumpled on the edge around the 

 cavity, so as to end in two, three, or even four more or less circular mouths." A magni- 

 ficent delineation of the elegant sponge completed this accurate diagnosis. 



In the systematic review of the sponges, which Gray gave in the Proceedings of 

 the Zoological Society London, in 1867, he placed Myliusia in the family of the Dactylo- 

 calycidae (" sponge massive, expanded or flabellate, the network with angular meshes,") 

 close to Dactylocalyx, and briefly characterised it on page 506 in the following words : — 

 " The sponge conical, cup-shaped, pierced with numerous short truncated tubes, forming 

 raised folded anastomising laminse on the lower surface." 



A diagnosis of the genus Myliusia, Gray, founded for the most part on the micro- 

 scopic structure of the skeletal framework, was published by Bowerbank in 1869 in the 

 Proceedings of the Zoological Society of London, part i. p. 66, and ran as follows : — 

 " Skeleton siliceo-fibrous. Fibres solid, cylindrical. Rete symmetrical, disposed in a 

 series of crypt-like layers parallel with the external surface, with intervening plades of 

 perforated siliceous tissue." 



Wyville Thomson,^ in his scheme of Porifera vitrea, rejected Gray's genus Myliusia, 

 and referred the form in question simply as Dactylocalyx callocyathus to the genus 

 Dactylocalyx. Moreover, Bowerbank" subsequently found, "on microscopic examina- 

 tion of the structure of the type specimen of Myliusia, Gray," that it was identical 

 with that of his genus Iphiteon. He therefore referred Gray's Myliusia callocyathus, as 

 Iphiteon callocyathus to the genus Iphiteon. Thus, then, the generic name Myliusia 

 became as it were free, and Bowerbank availing himself of the fact, designated another 

 recently studied remarkable Hexactinellid from St. Vincent, West Indies, with the 

 generic title Myliusia, and added to it the specific name grayi. The accurate descrip- 

 tion of the new species Myliusico grayi, Bowerbank, which was illustrated with two good 

 figures of the microscopic structure of the skeleton, undoubtedly showed the essential 

 difference between this species and Gray's iH7//i"«siacaifoc?/a^/iW5, and certainly established 

 the generic distinctness of the two. It is, however, very much to be regretted that 

 Bowerbank did not invent a new name for his new genus, as many errors and ani- 

 V)i(i;uities would thus have been avoided. 



Later authors have, however, by no means always attended to the essential difference 



' Phil. Trans., p. 713, 1869. -Pm. Zool. Soc. Load., \\ .335, 1869. 



(ZOOL. CHAIX. EXP. —PART LIII. — 1887.) Ggg 45 



