NEBELA MAEGINATA. 109 



sharp edge, or keel, confined to the upper half of the 

 test, whilst N. tubulosa has its entire margin, from 

 the crown to the mouth, margined or roughly carinated, 

 with an irregular edge. In the latter species the 

 sides are convex down to a point where the test be- 

 comes narrowed and a short but distinct neck is formed. 

 This perhaps, more than any other feature, distin- 

 guishes N. tubulosa from the species under considera- 

 tion. N. marginata, moreover, is destitute of any 

 marginal pore, and in narrow lateral view the test is 

 more abruptly conical. 



7. Nebela tubulosa Penard. 

 (Plate .XXVII, figs. 3 and 4 ; and fig. 93 in text.) 



Nebela collaris (pars) LEIDY Fresliw. Rhiz. N. Amer. p. 147, 



t. xxiii, ff. 1-6. 

 Nebela tubulosa PENARD in Mem. Soc. Geneve, XXXI (1890), 



2, p. 159 ; Faune Rhiz. Leman (1902), p. 353, ff. 1-5 (p. 



354) ; and in Pr. R. Soc. Edinb. XXV, 8 (1905), p. 594 ; 



SCHOUTEDEN in Ann. Biol. Lacustre, I, 3 (1906), p. 355 



(note) ; MURRAY in Ann. Scott. Nat. Hist. 1907, p. 95. 



Test in broad view arcuate above; its sides bi- 

 convex, except where they converge to form the neck ; 

 the body presenting a more or less ovate outline, and 

 the neck truncated at the extremity. The lateral 

 margins, both of the sides and crown, acute, so that a 

 sharp edge is produced all round, of which the outline 

 is more or less broken. Test bi-convex in transverse 

 view, its apex acute, and the neck, at about one-third 

 the length of the test from the mouth, with a marginal 

 perforation on each side, marked generally by a slight 

 swelling; the pore sometimes hardly perceptible in 

 the living animal, but careful examination will 

 generally reveal it. The entire envelope tinted a 

 chocolate-brown, which deepens with age; in the 

 upper portion with a surfacing of variously- shaped 

 transparent plates, sometimes distinct, but in other 

 cases faint in outline, oval or quadrangular, and 



