ss 
VINE : BRITISH PALAEOZOIC CTEXOSTOMAToUS POLYZOA. 
are also visible. This feature is shown in fig. 9, pi. 12 (Yorksh. 
Geol. and Polyt. Soc. vol. ix.) 
Locality and Horizon : Upper Silurian; Buildwas Beds ; Wenlock 
Shales, on stems of crinoids and broken shells. 
Ascodictyon radiciforme, Vine, differs in many respects from 
A. radians, the carboniferous form described by Nich. and Eth., 
June (Ann. Mag. Nat. Hist.. 1877, p. 465). In the Silurian species 
the peculiar pit-Ike structure, so admirably depicted in A. radians 
(ibid. pi. 19, fig. 10), is absent in all the examples that I have 
studied, and the stolons connecting the root-like vesicles are different 
in both species. The filamentous threads of A. radiciforme, Vine, 
are similar to the threads or stolons figured in the carboniferous, 
A. YouiKji, of the present paper £pl. 2, figs. 3-4). 
Ascodictyon siluriense, Vine, pi. 2, fig. 1. 
1881. Ascodictyon stellatum, Vine, Quart. Jour. Geol. Soc, p. 618. 
1882. ., var. siluriense, Vine, ibid., p. 52, figs. 1-2. 
1884 „ ., „ Vine, Ann. Mag. Nat. 
Hist. (August), p. 81. 
1887. „ „ „ Vine, Proc. Yorksh. Geol. 
Soc, vol. ix., p. 184, pi. 12, fig. 6. 
Zoarium composed of ovoid or fusiform vesicles, generally dis- 
posed in stellate clusters, and united in their colonial growths by 
hollow filamentous threads. Vesicles smooth and devoid of any 
special aperture or foraminated surfaces, similar to A. ateWitum, as 
figured by the authors of that species,* The vesicles of the Silurian 
species vary in size from one-fifth to one-sixth of a line in length, 
whilst the vesicles of A. stellatum, derived from the Devonian rocks 
of Ontario, vary in length from one-third to one-fifth of a line in 
length. As certain special features referred to their species by the 
authors, are entirely absent in the Silurian fossils, this necessitates the 
removal of the word "variety" from my present revision of this 
peculiar group of organic forms. 
Horizon : Upper Silurian ; Buildwas Beds of Wenlock Shales. 
* Ann. Mag. Nat. Hist., ser. 4, vol. xix., pi. 19, figs. 1-6. 
