﻿STACHEIA. 



109 



may be joined end to end more or less compactly, or may be connected by delicate tent- 

 like stoloniferous tubes, single or branching ; or each individual segment may represent 

 an entire animal, the test sometimes having an aperture placed at the end of a tadpole- 

 like tail, sometimes having no visible orifice. The adherent rougher Lituolce have 

 received the sub-generic name Placopsilina, and they present much the same range of 

 morphological variation as the adherent Trochammina, but they are always coarse and 

 rough in shell-texture. The segments are also usually more closely packed, and in 

 early growth they show a tendency to take a spiral arrangement. The trochoid and 

 plano-convex species of Valvulina appear to be all constructed for parasitic growth, but 

 except the very conical forms they are seldom found actually adherent. 



The genus Polyphragma 1 represents typically an irregularly cylindrical, sub-arenaceous 

 test, attached by one end, and growing in a curved or nearly erect line. It is composed 

 of a single series of superimposed discoidal segments, the aperture taking the form of a 

 number of perforations, arranged in more or less regular rings, on the convex face of the 

 terminal chamber. 



Turning now to the Perforata, — in the first division (family Lagenidd), the genus 

 Poli/morphina alone presents adherent forms, and these appear as aberrant modifica- 

 tions of well known free varieties. In the Poli/morphina concava of Williamson the 

 adhesion is effected by the convex side of the shell, whilst in the " rooted " forms 

 figured in the Monograph of the genus, 2 the attachment is secured by the fistular shelly 

 outgrowths. 



In the family Globigerinida the most prominent parasitic types are Carpenteria, 

 Planorbidina, and Polytrema, though the smaller Discorbina and perhaps other plano- 

 convex and trochoid Rotalians may occasionally be found growing upon foreign bodies. 



Carpenteria is essentially an irregular encrusting Globigerina, its relationship at times 

 attested by a disposition to assume a spiral arrangement in some of its segments ; but 

 more frequently consisting of a confused mass of chambers with large conspicuous 

 perforations. The plano-convex and outspread Planorbidina are probably normally 

 parasitic, as well as a section of the sub-generic group Truncatulina ; and even the allied 

 genus Tinoporus possesses an adherent variety, noticed on a later page as an isomorph of 

 one of the varieties of Stac/ieia. 



"Of all Foraminifera " observes Dr. Carpenter (Introd. p. 235) " there is none so 

 decidedly Zoophytic in its form and habit as Polytrema, for although it sometimes spreads 

 itself on the surfaces of shells, corals, &c, it not unfrequently rises from those surfaces in 

 an arborescent form, whilst sometimes its stalk instead of branching, swells into a globular 

 protuberance, which leaves a strong resemblance in size and general aspect to the 



1 Pohjphragma cribrosum, Keuss, 1872, ' Das Elbthalgebirge in Sachsen,' Iter Theil, p. 139, pi. xxxiii, 

 figs. 8—10. 



2 Brady, l'arker, and Jones, ' Trans. Linn. Soc. Lond.,' vol. xxvii, pi. xlii, figs. 38, 



