﻿STACHEIA. 



117 



Stacheia congesta, nov. PI. IX, figs. 1 — 5. 



Characters. — Test adherent, forming minute, elongate, subcylindrical, rounded, or 

 fusiform masses clustered around foreign bodies, preferring those of slender columnar 

 shape. Chambers very numerous ; irregular in shape, closely packed, confused in 

 arrangement ; the boundary-walls of those composing the superficial layer sometimes 

 indicated by the areolation of portions of the exterior of the test. Surface otherwise 

 granular or nearly smooth. Length to yg- inch (0'7 to 1-5 mm.). 



This species bears considerable resemblance to the smooth variety of the Rotalian 

 genus Tinoporus (T. lavis, P. and J.), not only in general external appearance and 

 occasional superficial areolation, but also in the mode of aggregation of its constituent 

 chamberlets, the prima facie difference being that the one is, the other is not, a parasitic 

 form. Not that the adherent condition is unknown in the genus Tinoporus : a 

 variety has already been alluded to which bears the same sort of resemblance to Stacheia 

 acervalis that Tinoporus Icevis bears to Stacheia congesta. Such analogies are not merely 

 interesting, but are of considerable value as collateral evidence in an order of animals 

 characterised by the tendency to isomorphism amongst its constituent groups. 



The drawings, PI. IX, figs. 1 — 4, are good representations of average examples of this 

 obscure organism ; fig. 5 is its longitudinal section, as seen by transmitted light ; the magni- 

 fying power employed is the same throughout, 50 diameters. The further enlargement 

 by means of higher powers brings out but little additional detail, owing partly to the granular 

 texture of the test and partly to the obliterating effect of the mineral infiltration. 

 Specimens areoccasionally met with having prominences like the arborescent growths 

 of Stacheia polytrematoides, but these appear to have taken their form from that of 

 the foreign body upon which the shell has grown. 



Distribution. — Specimens of Stacheia congesta have been found in a single locality in 

 the lower division of the English Carboniferous Limestones, but in the higher portion of 

 the series it is much less rare. In Scotland, on the contrary, it has been observed in two 

 or three localities of the Lower Limestone Group, whilst its presence in later beds has 

 only been clearly established in a single habitat. 



