ASTRORHIZIDAE 71 



Walls thicker and composed of coarser material, rough in texture, apertures incon- 

 spicuous. Length 1-2 mm., breadth 0-5 mm. 



The genotype Hippocrepinella hirudmea was not recorded at either St. 660 or WS 32. 

 Its place appears to be taken by a forin which we prefer to regard as a variety, rather 

 than as a separate species, although its appearance is very distinctive, especially in the 

 case of the specimens from St. 660, which is in Cumberland Bay. The specimens from 

 WS 32 are less rough. The organism is rare at both stations. 



84. Hippocrepinella alba, Heron-Allen and Earland (Plate VII, figs. 10-12). 



Hippocrepinella alba, Heron-Allen and Earland, 1929, etc., FSA, 1932, p. 259, pi. i, figs. 16-18. 

 Seven stations: 27, 45, 126, 144; WS 33, 154; MS 68. 



Test monothalamous, cylindrical or fusiform, furnished with a large principal aperture 

 on a produced neck, with or without a collar ; a secondary basal aperture may be present ; 

 wall very smooth and of paper-hke thinness, constructed of very minute particles 

 without visible cement. Inner cavity enormous compared with the thickness of the wall. 

 Colour uniformly dead white. 



Size very variable, the largest specimen being 0-30 mm. broad and 2-80 mm. long, 

 and the smallest 0-52 mm. long and 0-09 mm. broad. 



The above account is an attempt to describe an organism which, owing to its rarity 

 and fragility, is represented by very few entire specimens, hardly any of which agree in 

 all details, though all conform in the nature of the test. 



The wall of the test is extremely thin in comparison with the size of the organism, and, 

 owing to the absence of cement and the uniformly minute size of the particles employed 

 in its construction (apparently fragmentary Diatoms), is, when dry, fragile to the last 

 degree. In life it is almost certainly flexible and distensible, but nearly all our specimens 

 are more or less collapsed and broken. 



The great variation of specimens in size probably represents stages of growth only, 

 although there is an equally remarkable range of form between broadly fusiform and 

 elongate cylindrical. 



The most striking point of difference in the specimens lies in the form of the aboral 

 extremity. The principal aperture is always large and conspicuous on its more or less 

 produced neck and is sometimes furnished with a thickened collar. The secondary or 

 basal aperture hardly exists, as such, at all. In many specimens the basal end is pro- 

 duced into a pronounced nipple, which may or may not be pierced ; in other specimens, 

 it presents an unbroken rounded extremity. 



These points of difi^erence, especially the last mentioned, raise the questions whether 

 (i) the specimens represent more than one species, and (2) whether they are proper to 

 Hippocrepinella. We think the second point must be left for final decision when more 

 material is available, but having regard to the identical nature of the wall in all the 

 specimens and its probable plastic nature when living, we attach little importance to the 

 variations in size and shape, or even to the apparent suppression of the basal aperture. 



