160 rORAMINlFERA OF THE CRAG. 



Characters. — A small hyaline Textilarian shell, beginning with a flat spire, and 

 growing on with regular biserial chambers, making a narrow and somewhat 

 compressed test, of uniform width, and with rounded edges. 



The name Spiroplecta rosula was given by Ehrenberg to a (hyaline ?) shell 

 resembling in general contour the arenaceous form subsequently described by 

 Parker and Jones (' Phil. Trans.,' 1865, vol. civ, p. 370, pi. xv, figs. 23, 24) under 

 the name Textularia agglutinans, var. biformis. 



On the same plate with Spiroplecta rosula in the ' Mikrogeologie,' Ebrenberg 

 figured an allied form, but widening out in its growth (after the manner of Text, 

 gibhosa) as 8p. Americana. This was at first regarded by him as a Textilaria, but 

 its name was changed to Heterohelix in the ' Abhandl. Berliner Akad. Wiss.' for 

 1841 (1843), p. 429, No. 302; see also the 'Mikrogeol. Inhalt des Atlas,' 1854, 

 p. 22. At page 24 of the same index it is referred to as Spiroplecta Americana 

 from the Chalk of Missouri and Mississippi. It is doubtful if the test of this form 

 and of Sp. rosula (also from the Chalk of Mississippi) is represented as hyaline or 

 opaque in this plate ; and Ehrenberg nowhere defines their shell-structure. 

 Dr. H. B. Brady found that in recent specimens of Sp. Americana " the walls are 

 thin and smooth, and in small specimens hyaline " (op. cit., p. 376). Clear-shelled 

 forms like Sp. rosula have been found in existing seas. Of these recent 

 " species," some mentioned above are Sp. demersa, Ehr., from the Philippines ; 

 and Sp. nana, Ehr., from Florida ; of the latter there are (1) one of irregular 

 growth, and (2) a young individual. 



Other closely related hyaline forms are — 



Spiroplecta ahyssorum, Ehrenb., 1873. ' Monatsber. k. Preuss. Akad. Wiss.' for 

 1872, p. 293 ; ' Abhandl. Berl. Akad. Wiss.' for 1872, pp. 144 and 247 (Atlantic 

 Telegraph- Line). 



Sp. Gapensis, Ehrenb., 1873. Ibid., p. 294 ; and ibid., p. 247 (LaguUas Bank). 



Sp. ? profundissima, 1873. Ibid., p. 294 (Coral Sea). Imperfect individual. 



Ehrenberg also noted and figured in 1856, ' Abhandl. Berl. Ak. Wiss.' 

 (Physikal) for 1855, p. 169, pi. iv, fig. 13, a glauconitic cast of "Spiroplecta 

 ? " from the Zeuglodon Limestone of Alabama. 



Occurrence. — Recent specimens of Spiroplecta are of rare occurrence, and are 

 usually confined to the shallow waters of northern seas. These are, moreover, 

 usually arenaceous ; but the hyaline form, S. rosula, has been found on the north- 

 east coast of England (Brady) and in the Philippine seas (Ehrenberg). In the 

 fossil condition S. rosula has been recorded from the Cretaceous series of North 

 America (Ehrenberg), and from the PHocene beds of St. Erth (Millett). One 

 specimen only has been found in the Coralline Crag, and that from Gedgrave, 

 zone f. 



