GASTROPODA. l"i~' 



: 



prupoM the specific name erpaium. As wo understand It, /;,.. .H,..,,,I, , i. Mention rihe typp 



ii 1 ... I M //. r .-..-( -if.i. .lit!. -nut: mainly In thK that the aperture I- abruptly iiml nrvatly expanded 

 t Intervals .1- growth proceeds. The old expansions are either all broken away, or, a* i- more III 

 rtfabsorbiil. giving a condition iin-rUely SH In Trtmanntta. Each expansion. |H, i it* mark <>u 



r of tin- shell as may be sera from the cast of th.- Interior d|{ured above (Km. We). In 

 CnuptdottotMi, ' B, which also has an expands! mouth, i he expansion or border differs In being 



cut <>ut on ill.- liiin-r side sou to leave two projecting spurs, and In being developed at one the 

 l only. 



Genus TimciloNK.MA, Suiter, 



Troffuntemti and B**ma of SAI.TKIC, 1859, Cao. Org. Rem., Dec. 1, i 

 MEBK, 1875, Pal. Ohio, vol. I, p. 219. 



(part.) of HALL, SALTKK and other*. 



Shell turliinate, umbilicated; spire varying in bight, base generally flattened 

 yet sometimes quite ventricose; whorls not numerous (4 8), varying from strongly 

 angular to rounded, always with two more or less prominent ridges or angles 

 between which lies a broad vertical, usually flat or concave, peripheral space; a third 

 n-l.u'i 1 usually near the suture, while a fourth generally surrounds the umbilical 

 cavity. Other, but smaller ridges may occur though chiefly on the basal half of the 

 whorls. Lines of growth crossing the whorls from above obliquely backward, often 

 vertical and not infrequently inclined in the opposite way on the peripheral band. 

 In the last case the outer lip is broadly notched at the extremity of the upper 

 peripheral angle. Aperture usually very oblique; peritreme complete; inner lip 

 varying in thickness, not reflected. Type, T. umbilicatum Hall sp. 



This excellent genus exhibits considerable variety in its contents. There is 

 scarcely a single character that pertains strictly to all the species, yet, comparing 

 one with the other, we Hud them so closely knit together that to separate them very 

 far would mean nothing less than violence to natural classification. We do not 

 mean to say that the genus may not be conveniently and yet naturally divided, or 

 subdivided, if that is preferable. Eunetna, Salter, the type species of which is 







scarcely more than a high and practically imperforate Trochonema, was established at 

 the same time as Trochonema. As at present understood, Kunemn is not a well-marked 

 genus, while its employment even as a subgenus is attended with difficulties. It 

 cannot be maintained on Sailer's characterization, since in shells of this type the 

 relative size of the umbilicus is a very unreliable generic character. However, if we 

 will select another character of /.'. xtri</illntum, viz.: the very slight obliquity of its 

 aperture, the group may have some value. A much better division may be instituted 

 for the reception of the group of species typified by our T. puli-hdlum which eventu- 

 ally gave origin to Cyclonema. The separation of this group is certainly convenient 

 since it leaves Trochonema (. t.) as a more compact and sharply defined group. 

 Brief definitions of these divisions follow: 



