Surcula.] GASTROPODA. 487 



out on the line of the ribs into a high-shouldered prominent wing, 

 between which and the body -whorl the broad deep and rounded 

 sinus lies ; toward the front of the. mouth it retreats rapidly to the 

 point of the canal. Columella long, straight, narrow, slightly twisted 

 below. Inner Up rather broad, a little thickened, with a slightly 

 raised edge. Operculum unknown. (Watson.) 



Diameter, 19 mm. ; height, 44-5 mm. 



Animal unknown. 



Type in the British Museum. 



Hab. East of East Cape, in 700 fathoms (" Challenger "). East 

 Africa, near Dar-es-Salam, in 2,559 metres (" Valdivia"). 



Subfam. 3. BORSONIN.E. 



Columella plicate or subplicate. Operculum with the nucleus sub- 

 apical (in Bathyt.oma Cheesemani). 



KEY TO GENERA. 



A. Shell mitriforin ; sinus broad and not deep, near the suture ; 



columella generally with 2 plaits . . . . . . MITROMORPHA. 



B. Shell oval, ventricose ; sinus distant from the suture, deep ; 



columella subplicate or wrinkled . . . . . . BATHYTOMA. 



Genus 1. MITROMORPHA, A. Adams, 1865. 



Mitromorpha, A. Adams, A.M.N.H. (3), xv, 1865, 322. Type : M. lira/a, 

 A. Ad. 



Shell small, somewhat elongate and biconic, with revolving lirse 

 and sometimes axially plicate ; nucleus globose ; outer lip scarcely 

 or not at all notched above, often denticulate inside ; columella nearly 

 straight, generally having faint vestiges of oblique plaits, which do 

 not extend far into the shell. 



Distribution. Japan, California, Barbadoes, Porto Kico, Austral- 

 asia. 



Fossil in the Pliocene of France. 



KEY TO SPECIES. 



A. Shell with axial sculpture. Whorls with about 18 axial riblets, 



crossed by equidistant spiral cords, intersections gemmate . . gemmata. 



B. Shell with fine spiral lirae only. 



a. Spire of the same height as the aperture with canal ; whorls 

 shouldered ; protoconch spirally striate. Height about 

 16 mm. . . . . . . . . . . . . striata. 



aa. Spire about \\ times the height of the aperture and canal ; 

 whorls not shouldered ; protoconch smooth. Height 

 about 5-5 mm. . . . . . . . . . . subslriata. 



1. Mitromorpha gemmata, Suter, 1908. Plate 21, fig. 14. 



Mitromorpha gemmata, Suter, P. Mai. S., viii, 1908, 186, pi. 7, f. 18. 



Shell small, ovate, thin and fragile, semitransparent, axially 

 costate and spirally striate, the crossing-points gemmate. Sculpture : 

 All the whorls below the smooth protoconch are axially equidistantly 



