— 71 — 



Genus Hyalostelia, Zittel. 



(Handbuch der Palaeontologie p. 185). 



Hyalostelia fusiformis n. sp, 



(Plate V, fig. 12—16). 



Free hexactinellid spicules having one axis much longer 

 than the others, arms straight or but slightly curved, and 

 gradual!)' tapering to a point. The centre of the spicule 

 solid and inflated. Very variable in their dimensions. The 

 longer axis of the larger spicules is i ,05 mm. in length ; and 

 the central node 0.18 mm in thickness. A small spicule is 

 0,45 mm. long; and the central node 0,09 mm. in diameter. These 

 spicules are distinguished from the preceding form by the rapid 

 tapering of the arms and the prominent inflation of the central 

 node. In some examples the arms of the spicule are fusiform, and 

 they have the aspect of three robust aceratc spicules joined 

 together at right angles ; in others, the central node is more 

 of a spheroidal character and the arms are more distinctly 

 marked off from the centre. The smaller spicules are more 

 numerous than the larger in the deposit. 



The forms nearest to these spicules are those which have 

 been described by Messrs. Young from the Carboniferous strata 

 in Scotland under the name of Hyalonema Smithii , (An. 

 Mag. Nat. Hist. S. 4, Vol. 20, p. 435, PI. XIV). The Hor- 

 stead specimens are however much more regular in their form, 

 as well as much smaller than the Carboniferous spicules. The 

 peculiar fusiform inflation of the central node marks these 

 spicules off" very clearly from those of any known fossil and 

 recent species of this suborder. 



A spicule approximating in size to the smaller of my 

 specimens has been figured by Mr. Carter from the Haldon 

 Green Sand (An. Mag. N. H. S. 4, Vol. 7, p. 123, PI. VII, 

 fig- ' S) ^^^ ^^ compares it to the silicified fibre of the 

 Euplectellidae. A spicule with inflated node but with the 



