6 BULLETIN 71, UNITED STATES NATIONAL MUSEUM. 



f orate, occasionally so throughout the test, often with an external 

 coating of siliceous or calcareous sand, or in some species nearly the 

 whole test arenaceous; aperture typically an arched slit at the inner 

 margin of the chamber close to its line of attachment to the preceding 

 chamber; occasionally with the aperture surrounded by a raised lip, 

 or in some species with the aperture circular and terminal. 



The genus Textularia as usually considered includes species of 

 several different sorts which might perhaps be placed in separate 

 genera, as has been done by some authors. All have the same gen- 

 eral type of test in that the chambers, at least in the adult, are 

 arranged biserially, each chamber alternating with the immediately 

 preceding and succeeding chamber of the opposite side and connecting 

 with them, so that typically no chambers of the same series are con- 

 nected with one another except indirectly through the chambers of 

 the opposite series. In many species where a large series of speci- 

 mens can be obtained from a single dredging both the microspheric 

 and megalospheric forms of the species may be found. Here again 

 there is a considerable difference in the various groups. In the 

 typical arenaceous species the microspheric form has a definitely 

 coiled series of chambers about the small proloculum before the 

 biserial condition is taken on. This shows its relation to Spiroplecta 

 and to the coiled forms of the Lituolidae. In the megalospheric form 

 of the same species the biserial condition is usually taken on by the 

 two chambers immediately succeeding the large proloculum. As a 

 rule the megalospheric form is the more common, as is usually the 

 case in other groups. 



Other species, as T. quadrilatera, for example, may be found in the 

 two forms, but the difference is mainly in the size of the proloculum 

 and the number of succeeding chambers, in both cases the biserial 

 condition being taken on with the two chambers following the 

 proloculum. 



Usually in species of Textularia there is a regular increase in the 

 diameter of the test with the addition of new chambers, but in some 

 individuals there is a definite senescence, in which the chambers of 

 the later portion are smaller and the diameter of the test actually 

 reduced. 



In an end view it is usually seen that the lateral portions of the 

 newly added chamber extend beyond the aperture on either side so 

 that the aperture in the end view seems to be in an indentation of 

 the inner margin of the chamber. This is especially true of those 

 species that have the aperture a slitlike opening on the inner margin 

 close to the line of meeting with the previous chamber. In those 

 species in which the aperture is not so elongate and is farther from the 

 previous chamber, this indentation is much less marked or wanting, 



