VINE : BRITISH PALEOZOIC CTENOSTOMATOUS POLYZOA. 91 
adherent to a portion of a Crinoid stem (Plafycrinus, sp.), and the 
stellate vesicles are not so abundant in their colonial growths as in 
the Silurian species. 
Horizon and Locality : Low. Carboniferous Shales ; Hairmyres, 
Scotland. 
This species is named in honour of Mr. John Young, of the 
Hunterian Museum, Glasgow, to whose kindness in supplying me with 
washed and unwashed Carboniferous shales, I owe so much. The 
form described I have only met with in the Hairmyres shales, where it 
is very rare. I have placed the clusters of vesicles of the fossil form of 
A. Youngi by the side of the recent Valkeria tuberosa, Heller, for the 
purpose of comparison. In the one case vesicles and filamentous threads 
(fig. 3) are magnified to about the same proportions as figs. 1 and 2 on 
the same plate ; the other (fig. 4) is magnified about 60 times. The 
abraided surfaces, however, shown in figs. 3 and 4, must not be regarded 
as normal features, but by means of this abrasion we may indicate 
that the vesicles were organically hollow, and the dark mass (pyrites ?) 
which exists below the outer covering probably represents the once 
existing animal matter in the several vesicles, but this suggestion 
must be regarded as a conjecture only. The type character of the 
vesicles are generally unlike all the other species that have been 
figured, and it seems to me that A. Youngi is more closely allied to 
the type vesicles of Valkeria than to other forms. Both figures 3 
and 4 are drawn by the aid of the Camera lucida, only to different 
scales, which are indicated by the magnified portions of the parts of 
one hundredths of an inch. 
Genus Rhopalonama, Ulrich. 
1890. Geological Survey of Illinois, vol. viii., p. 367. 
Derivation Rhopalon, a club. 
Cells slender, fusiform, arranged in a single anastomising series. 
Cell mouths small, near one end of the cell. Type R. venosa, Ulrich ; 
range Trenton and Cincinnati. 
As this is defined and limited to the type specimen, it will be 
impossible for me to include any of the British species in this genus. 
Rhopalonaria venosa* is defined thus : " Cells uniserial, long, acutely 
* 1879 Jour. Cincin. Soc. Nat. Hist., vol. ii., pi. 7, figs. 24-24 . 
