. GASTROPODA. 945 
Omospira laticincta.] 
plate LXIX). As may be seen in fig. 65 on plate LXX, this is not the case in 
Omospira, the lines in this case crossing obliquely and increasing iu curvature 
downward. The lines on the band, furthermore, are of the same character as those 
above the band, only curved in the opposite direction, the two portions united 
forming a sigmoid curve as in Raphistomina; and their continuity is interrupted 
when the change in direction occurs by a raised line,as is frequently the case in 
Raphistoma. Is it fair to explain the conditions observed in Omospira by supposing 
that they have resulted, first, through the elevation of the spire and the consequent 
reduction of peripheral carina and hightening of the volutions, and second, either 
by a mere approximation toward the prevailing character of the Gastropoda with 
which they are chiefly associated, or by following the more prevalent tendency 
which they, as Raphistomide, inherited, like the Pleurotomariide, from their common 
ancestor? For the present we must confess that we have allowed such theoretical 
reasons as the foregoing to dominate our placement of the genus. 
To whatever position Omospira may be ultimately assigned, the validity of the 
genus is not likely to be seriously affected. If it really belongs to the Raphistomide, 
then it will stand as a type obviously distinct from the other genera of the family, 
because of its high spire and comparatively rounded volutions. If, on the contrary, 
it proves to be one of the Pleurotomartide, then it will be readily distinguished by 
the peculiarities of the band mentioned in the preceding paragraph. The high 
position of the band would also serve in the latter association. 
As to the specific representation of the genus, we know of only two species that 
can be referred here positively, namely, the type O. laticincta and Murchisonia 
alexandra Billings (M. ventricosa Salter, not Hall). Possibly Hall’s M. ventricosa also 
belongs here, but Whitfield says it is a Lophospira. 
OmospirA LATICINGTA, ”. sp. (Ulrich.) 
PLATE LXX, FIGS. 64 and 65. 
Shell 50-60 mm. high; greatest width about three-fifths of the hight; apical 
angle varying between 49° and 55°, the angle formed by the first three or four 
whorls usually about five degrees more. Volutions about seven in number, obliquely 
flattened above, ventricose below, their sides almost vertical, the upper turns more 
rounded than the last three. Sometimes the flattened upper portion is more nearly 
horizontal than in the specimen illustrated. Aperture subtriangular, somewhat 
higher than wide, the outer lip thin and curving gradually inward from the shoulder- 
like upper angle to the narrowly rounded base; inner lip only moderately thick, 
nearly straight, and generally reflexed in its upper part over a minute umbilicus, 
—60 
