﻿STACHEIA. 



Ill 



mechanical difficulties attendant on its condition preclude exhaustive treatment and 

 necessitate a certain amount of reservation in respect to many points of detail. 



The disposition of the parts and their relative significance are readily seen in the 

 simpler forms by means of longitudinal sections. The segments arranged in linear 

 series are either distinct and convex, circular in section, and partially embracing, — or 

 else each succeeding segment almost entirely encloses those that have preceded it ; 

 in all cases the chamber cavities are subdivided by more or less regular secondary 

 septa. The most careful examination fails to yield any trace of true shell- perfora- 

 tion ; and, though in these simple varieties the surface of the test is nearly smooth, 

 there can be little doubt that its texture is precisely similar to that of Trocham- 

 mina and the allied arenaceous types in which the calcareous cement is largely in 

 excess of the embedded sand-grains. In point of fact, the external appearance of 

 the test closely resembles that of the fossil Valvulina of the same beds, and the 

 analogy between the peculiar subdivision of the segments in the simpler varieties of 

 Stacheia and the condition of the chambers in Valvulina Youngi is too striking to be 

 overlooked. 



This analogy is important in another point of view, for it suggests the solution of a 

 question of considerable difficulty, namely, the position and character of the aperture. 

 Were we dependent on Carboniferous specimens alone, it would not be easy to speak 

 with any certainty of the aperture in the genus Valvulina; but by the aid of recent 

 specimens its characters are easily determined, and we know that it takes the form of a 

 curved slit on the under surface of the test, hidden by a tongue-like shelly projection. It 

 is not possible to demonstrate the same condition in Stacheia, but there is quite sufficient 

 evidence to justify the assumption that the nature and position of the orifice are not 

 very widely different. In S. acervalis, for instance, it is pretty certainly on the under 

 surface of the test, and it has even been noticed in the form of a produced neck 

 {Planorbulina fashion) apparently springing from the lower side of the last segment. It 

 would seem to follow, therefore, that in varieties like 8. marginulinoides and 8. fusiform is, 

 in which the segments are ring-shaped and embracing, the pseudopodia would protrude 

 at the end of the test around the sides of the body upon which the organism has grown, 

 or, in case of the decay or disintegration of the columnar support, sarcode would occupy 

 its place and the open end would form the general aperture. This would furnish a not 

 improbable explanation, the only one I am able to suggest of the otherwise obscure cha- 

 racters of the simpler modifications of the type. 



The interior structure of the two species which are formed of a large number of 

 minute chambers is more obscure, and it is possible that further investigation may show 

 reasons for placing them in a subordinate group by themselves. Of the two, Stacheia 

 congesta is the more complex, and it will be best understood by reference to what is 

 known of the compact varieties of the Rotaline genus Tinoporus (especially T. Icevis, P. and 

 J.), to which it bears considerable analogy, the fact of its growing in adherent masses 



