LITUOLIDAE 109 



Sub-family SILICININAE 

 Genus Spirolocammina, gen.n. 



Test minute, compressed, consisting of several pairs of chambers arranged on a 

 spiroloculine plan, but with a very slight sigmoiline curve in the long axis. Aperture 

 terminal, on a produced neck, without tooth. Test composed of extremely minute 

 mineral particles imbedded in a chitinous wall, and resistant to acid. Wall of test thin, 

 smooth but not polished. 



The fact that the test is not in any way affected by treatment with hot nitric acid, the 

 thin chambers remaining uncoUapsed, proves the absence of any calcareous constituent 

 and its close relationship to Miliammina. Four of the plans of growth associated with 

 the calcareous Miliolidae have now been shown to occur also in the Silicininae, viz. the 

 spiroloculine in Spirolocammina, the triloculine and quinqueloculine in Miliammina, and 

 the sigmoiline in Silicosigmoilina . 



215. Spirolocammina tenuis, sp.n. (Plate IV, figs. 13-16). 

 Six stations: 360, 382; WS 199, 400, 472, 502. 



Test minute, compressed, consisting of two to three pairs of tubular chambers arranged 

 in a spiroloculine plan on opposite sides of the long axis of the test. Walls of the chambers 

 thin, smooth but unpolished, nearly white in colour, composed of extremely minute 

 mineral particles and probably diatomaceous fragments, imbedded in a chitinous mem- 

 brane. Edge of the test round, the chambers being tubular in section, somewhat 

 enlarged at the aboral end where each chamber envelops and encloses the produced 

 tubular neck of the preceding chamber. Aperture round and simple, at the terminal 

 end of the produced neck. The test is not affected in any way by treatment with hot 

 nitric acid. 



There is a very slight sigmoiline curve in the arrangement of the chambers, hardly 

 noticeable except by oblique illumination, and not in any way comparable with the 

 pronounced spiral of Silicosigmoilina. Length up to 0-55 mm. ; breadth 0-15 mm.; 

 thickness 0-05 mm. 



This is a very interesting little form which was at first thought to be a pauperate 

 condition of Sigmoilina tenuissima (Reuss) (see No. 30); but its distribution is quite 

 distinct, that species being confined to deep-water stations nearer the Antarctic con- 

 vergence line, while Spirolocammina tennis was found only in the deep water of the 

 Scotia and Bellingshausen Seas, well inside the area of pack-ice. 



The acid test is a conclusive proof of the distinction between the two forms ; Sig- 

 moilina tenuissima is instantly destroyed with effervescence, while Spirolocammina tennis 

 is unaffected. 



Spirolocammina tennis is very rare, even at the few stations where it was recorded, but 

 a considerable number of specimens were found in all, the majority at St. WS 199. At 

 St. 360 two specimens were found, one much larger than usual, the other malformed, 

 the final chamber being out of the usual axis of growth. In depth the species ranges 



