﻿STACHEIA. 



115 



Stacheia pupoides, nov. PI. VIII, figs. 17 — 27. 



Characters. — Test adherent, elongate, tapering, uniserial ; composed of a line of 

 irregular convex segments, either lying flat on the surface of a foreign body, or embracing 

 it to a greater or less extent. Segments inflated ; interior cancellated, or subdivided more 

 or less regularly. Surface granular or nearly smooth. Length inch (TO mm.). 



Typically, Stacheia pupoides consists of a line of convex, tent-like, adherent 

 chambers, each chamber embracing its predecessor somewhat, and subdivided in its 

 interior. The external aspect of average specimens is well shown in PI. VIII, 

 figs. 20 and 22 ; their internal structure in figs. 26 and 27. Modifications of the normal 

 form probably depend more on the nature of the body that serves for a support than on 

 any inherent tendency of the animal. If the support be thin and slender, the shell 

 embraces it more or less completely, and the margins of the chambers approximate on 

 the opposite side, as in figs. 24, 25, &c. The central body may have been a fragment of 

 organic matter which has been speedily decomposed ; and in this case, which is not an 

 unusual one, the margins of the segments may meet and form a nearly cylindrical test, the 

 line of union being only indicated by a slightly excavated longitudinal suture, as in 

 figs. 21 and 23. 



Some two or three specimens have been found pertaining to this category, but 

 with thin and compressed, rather than cylindrical, contour (fig. 17). These appear to have 

 lost all trace of the central support, except, perhaps, just at the narrow end, and the 

 interior of the test is filled up with cancellated shelly growths. Longitudinal sections 

 exhibit the minuter structure very beautifully ; they bear a high magnifying power with 

 advantage (fig. 19), and show the communication between the chambers much more 

 satisfactorily than any similar sections yet obtained from the commoner variety. 



The general aperture of the test of Stacheia pupoides is probably analogous in its nature 

 and position to that of S. marginulinoides ; and, if what has been suggested with regard 

 to that species be correct, it should be on the under or inner surface, near the margin of 

 the terminal segment. 



Distribution. — In England this species has been met with both in the higher and 

 lower division of the Carboniferous Limestone rocks, in Scotland, in the Lower 

 Limestone Group only ; but in none of the six localities in which it has been found is it 

 at all common. 



