HYALOSTELIA. 109 



Group. — Lyssakina. 



Family. — Pollakid2E. 



Genus. — Hyalostelia, Zittel ; Emend. Hinde. 



1878. Handbuch der Palasontologie, Bd. i, Lief. 2, p. 185. 



Syn. — Pyritonema, M ' Coy ; Acestra, F. Boemer ; Acanthospongia, Young (non 

 M'Coy) ; Hyalonema, Young, Carter (in part) ; Serpula, Portlock, M'Coy (in part) ; 

 Astroconia ? Sottas. 



Generic Characters. — Complete form of Sponge unknown ; the body-portion is 

 composed partly of simple hexactinellid spicules in which one axis is usually much 

 elongated, and partly of spicules in which one or more of the rays are inflated, 

 spined, reduced to rounded knobs, or even absent. The dermal layer is mainly 

 formed of large spicules in which the distal ray is reduced to a blunted process. 

 The anchoring appendage consists of elongated, cylindrical, rod-like spicules, 

 which are either separate, or in rope-like bundles, and sometimes terminate in four 

 recurved rays. 



This genus was based by Prof. Zittel on the characters of Hyalonema Smithii, 

 as described by Messrs. Young and Young. 1 These authors, however, included in 

 the type-species a great variety of forms of detached spicules, some of which 

 belong to distinct genera. Thus, for example, the spicules with from six to eight 

 horizontal rays, mentioned in Zittel's diagnosis of the genus, do not belong to the 

 same Sponge as the simple hexactinellid spicules. This has been proved by the 

 subsequent discovery of fragments of spicular mesh, in some of which hexactinellid 

 spicules and their modifications are exclusively present, whilst others are composed 

 only of the umbrella-shaped spicules with numerous horizontal rays. 2 I have 

 therefore proposed that the skeletal-spicules in Hyalostelia Smithii, which has 

 been taken as the type of the genus, should be restricted to such simple and 

 modified hexactinellids as are present in the connected fragments of skeleton, and 

 that the umbrella- and stellate- spicules should be excluded from it. The body- 

 spicules do not appear to have been originally attached together in any way ; 

 those occurring in the fragments of the skeleton which have been met with are 

 held together by a secondary deposit of silica. 



The elongated anchoring spicules of the Sponge are present in great abundance 

 in the same beds with the body-spicules, and are therefore assumed to have 



1 • Ann. and Mag. Nat. Hist.,' ser. 4, vol. xx, p. 425, pis. xiv, xv. 

 3 ' Cat. Foss. Sponges,' p. 150. 



