DISCORBINA ORBICULARIS. 295 



anterior and peripheral borders, imparting thereby a lobulate outline to the 

 margin of the shell. Anterior border of each segment overlapping the posterior 

 portion of that immediately in front of it. Inferiorly the outlines of the segments 

 less distinct, usually marked by irregular sinuate lines extending from the peri- 

 phery to the umbilicus or near it. Aperture a long, narrow, arched fissure on 

 the inferior umbilical border of the ultimate segment. 



Occurrence. — Discorhina rosacea is exceedingly common, and according to the 

 ' Challenger ' Report, " within certain depths it is found in almost every sea, 

 from the shores of Shetland and the Faroe Islands on the north, to Magellan's 

 Strait on the south. Its home is on shallow bottoms, and it becomes rare at 

 greater depths than 250 fathoms ; but occasional specimens are met with as low 

 as 1000 fathoms." In contrast with this, Egger in his ' Grazelle ' memoir records 

 specimens from depths ranging from \\ to 2740 fathoms, and the larger number 

 of his records are from depths exceeding 1000 fathoms. The figures given by 

 Egger in his pi. xv, however, suggest a doubt m our minds as to the proper 

 identification of the species. 



The geological distribution of D. rosacea extends to the Neocomian (Bargate 

 Beds). Specimens have also been recorded from the Eocene (London Clay and 

 Calcaire Grossier), the Miocene of Vienna, Muddy Creek (Victoria), and Italy, 

 the Pliocene of Italy and St. Erth, and the Pleistocene of the British Islands and 

 the Island of Ischia. In the Coralline Crag we have specimens from nearly every 

 zone examined ; and, as recorded in the First Part of this Monograph, the shell 

 has also been found in the Upper Crag of Southwold, 



4. DiscoEBiNA OEBicTjLAKis {(V Orbignij), 1826. Plate VII, figs. 31 a—c. 



DiscoiiBis ORBicuLAiiis, (VOrl., 1826. Ann. Sci. Nat., vol. vii, p. 274, No. 35. 

 EosAMNA ORBICULARIS, (T Orl)., 1847-50. Prodrome, part 2, p. 407, No. 1.328. 



— — (?), Terquem, 1876. Plage Dunkerque, p. 75, pi. ix, figs. 4a, J. 



AsTEEiGEEiNA Ehodiensis, Terquem, 1878. Mem. Soc. Geol. Prance, ser. 3, 



vol. i, p. 31, pi. iii (viii),figs. 1 — 4. 

 DiscoRBis OEBicuLARiB, Bertlielin, 1878. Ann. Soc. Ac. Nantes, ser. 5, vol. viii, 



p. 242, No. 63. 

 DiscoEBiNA EOSACEA, Terrigi, 1880. Atti Accad. Pontif. N. Lineei, vol. xxxiii, 



p. 200, pi. iii, figs. 54, 55. 



— jiTNUTissiMA, Seguenza, 1880. Atti E. Acead. Lineei, ser. 3, vol. vi, 



p. 149, pi. xiv, figs. 1, 1 a, 1 h. 



— ORBicULAEis, Braihj, 1884. Eeport ' Challenger,' p. 647, pi. Ixxxviii, 



figs. 4—8. 



— — Balkwill and Milhtt, 1884. Journ, Micr., vol. iii, 



p. 23, pi. iv, fig.. 13. 



