-iTROPODA. -". 



Ommplr. l.iMi 



plate I \l\ As may be seen in fig. 65 on plate l.\\. tin- is not the case in 

 Omosi'i>-'t, tin- line- in this case croin^ obliquely and increasing in curvature 

 downward. The lines on the hand. furthermore, are of the same character as those 

 above tin- band, only curved in the opposite direction, the two portions united 

 forming a sigmoid curve as in /i'u/i/ji ,' ;';n; t - and their rout inuity is interrupted 

 when tlic change in direction occurs l>y ;i raised line, a- i- frequently the case in 

 I- it fair to explain tho conditions observed in Omospira by supposing 

 that they have resulted, first, through the elevation of the spire and the consequent 

 reduction of peripheral carina ami lightening 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 Raphisdnniilir, inherited, like the Plfurotomuriiiln, from their common 

 ancestor? For the pre-ent we must confess that we have allowed such theoretical 

 reasons as the foregoing to dominate our placement of the genus. 



whatever position Omospira may be ultimately assigned, the validity of the 



H is not likely to be seriously affected. If it really belongs to the Raphistoin 

 then it will >tand as a type obviously distinct from the other genera of the family, 

 because of it- high spire and comparatively rounded volutions. If, on the contrary, 

 it proves to be one of the PlturntniiKiriiilie, then it will be readily distinguished by 

 the peculiarities of the band mentioned in the preceding paragraph. The high 

 po-ition 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 0. luticinrtn and Murrhisonia 



n'lr-i Hillings tlter. not Hall). Possibly Hall's M. rmtricosa also 



Belongs here, but W bitfield says it is a 



OMOSPIRA LATICINCTA, n. sp. (Ulrich.) 



PLAT) 1 \\ FIGS. M *nd 



i '" i '.<i nun. high; greatest width about three-fifths of the bight: apical 

 angle varying l-etv. ' and ">", .the angle formed by the h'r-t three or four 



wliorU n-nally about live degrees more. Volution* a bout seven in number, obliquely 

 flattened above, ventricose below, their -ides ahno-t vertical, the upper turns more 

 rounded than the last three. Sometimes the flattened upper portion is more nearly 

 horizontal than in the specimen illu>trated. Aperture -nbtriangular, 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 umbilicu-. 



-60 



