﻿ENDOTHYRA. 



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General Characters. — Test free, spiral, rotaliform, more or less unsymmetrical 

 bilaterally. Segments numerous. Texture subarenaceous, imperforate, though usually 

 smooth externally. Aperture simple, situated on the inner margin of the terminal 

 segment close to the periphery of the previous circlet of chambers. 



The Rotaliform group, to which may be referred a considerable proportion of the 

 Foraminifera of the Carboniferous beds, forms collectively a very distinct and well marked 

 series notwithstanding the external resemblance that many of its members bear to 

 analogous forms amongst the true Rotalina, and the consequent difficulty in laying down 

 morphological characters, couched in brief zoological terms, that would not apply with 

 almost equal fitness to members of other genera. There is perhaps not one of the ten 

 "species" about to be described to which a parallel or isomorph might not be found either 

 amongst the Rotalina or in the genus Nonionina, or sometimes in both. Still there are 

 certain broad and important distinctions which are easily recognised. In general terms 

 Endothyra is lower in the scale of organization than any true Rotaline, and though it 

 might not be possible in every case to establish the relative position, say of two chance 

 individuals, one belonging to each group, the distinction is none the less real and readily 

 ascertained by the examination of a number of specimens. 



The texture of the shell in Endothyra is to a greater or less degree arenaceous ; that 

 is to say, built up of minute particles of sand (necessarily in these limestone seas, of 

 calcareous sand) embedded in a calcareous cement. The cement is not a dark ochreous 

 material such as is commonly secreted by the rougher Trochammince, nor are the particles 

 of sand large and angular, and in excess of the cement, as in some other Lituoline genera ; 

 but the grains are minute and rounded and set in a homogeneous material, so that it is 

 often only by the weathered or fractured surface that the built-up nature of the test is 

 rendered apparent. Sometimes the fine calcareous cement is in large excess, giving rise to 

 specimens with sutures thickened by bands of clear shell substance just as in the hyaline 

 Foraminifera. In comparison with true Lituola the test in Endothyra is generally very 

 thin, and, so far as yet ascertained, never exhibits the tendency to fill up the cavities of 

 the chambers with labyrinthic shelly growths from its inner surface. 



On the other hand the investment seems to be normally, if not invariably, imperforate. 

 It is impossible to speak with complete certainty, for the condition in which the specimens 

 are found — infiltrated with calcareous material of the same composition as the test itself — 

 is exceedingly unfavorable for the determination of minute characters. In point of fact it 

 is very rarely that even the general pseudopodial aperture, which transparent sections shoiv 

 to be of considerable size, is visible externally, much less any minute perforations that may 

 have existed in the shell-wall. Some of the more delicate varieties of the genus, such as 

 E. ammonoides and E. subtilissima, not unfrequently have a dotted appearance, which at 

 first sight looks very like shell-perforation ; but the use of high magnifying powers and 

 carefully adjusted light has always shown this to be due to a granular condition of the 



