PHOLIDOCLADIA. 81 



nodes at their point of junction. The dermal layer is formed of minute irregular 

 scale-like spicules, which ovei'lap each other to form a compact surface-covering. 



This genus is allied to Thamnosponffia in the general characters of the interior 

 spicular mesh ; but the spicular rays in this latter genus are not so strongly tuber- 

 ciilated, and the tubercles are not in a single series as in PhoUdocladia. It is 

 further differentiated from Thamnospomjia in the form of the spicules of the dermal 

 layer. The characters of the dermal layer ally the genus to Plinthosella, but the 

 interior spicules differ notably in their form, size, and disposition from those of 

 Plinthosella ; the mode of growth of the sponge itself is also very different. 



The only examples of the genus are from the Upper Chalk, preserved in the 

 interior of flints. 



Pholidocladia dichotomus, Hinde, n. sp. (Plate XX. figs. 5, 5 «, 5 b.) 



Sponge growing in a bush-like form, with somewhat slender branches, from 5 "5 to 

 8'5 mm. in thickness, which dichotomise at intervals. The branches frequently 

 coalesce when they come in contact with each other ; they are rounded at their 

 terminations. The only specimen, which is incomplete, forms a mass about 110 mm. 

 in height and 75 mm. in width. 



The spicular mesh of the interior is closely set ; the spicular arms are about 

 •3 mm. in length and -07 mm. in width. The dermal layer is only partially preserved ; 

 the scaly spicules composing it are very irregular in form — some are cii'cular or oval 

 with smooth or indented margins, whilst others are partially elongated : they are 

 about -5 mm. in width. Where thfe dermal layer is preserved the surface of the 

 stems is smooth. 



The specimen figured belongs to the Jermyn-Street Museum. 



Bistrihution. Upper Chalk: Wiltshire {Cunnington coll.). 



PnoLiDOCLADiA KAMOSus, Hiiide, n. sp. (Plate XVIII. figs. 5, 5 «, 5 b.) 



Sponge growing in bushy masses of small irregularly branching stems, from 2'5 to 

 3*5 mm. in thickness; branches rounded at their ends. The spicular mesh of the 

 interior is formed of very nodose spicules, with arms about '25 mm. in length and 

 •07 mm. in width. No dermal layer has been preserved. 



This species generally occurs in the form of small empty branching tubes in the 

 interior of flints, which would hardly be recognized as casts of lithistid sponges. 

 The sponge-stem itself is very seldom preserved ; but I fortunately found one or two 

 small fragments which left no doubt that these tubes were occupied by small 

 branching sponges, which had afterwards been dissolved away. The character of 

 the interior spicular mesh of this species so closely resembles that of P. dichotoma 

 that it is highly probable that, similar to that species, it also had a dermal layer of 

 small scales. There are several flints in the collection with tubes even smaller than 



M 



