1.4-1 



DM .I<>NK>KLI.A Unch. 

 .'-u.< r. Ml J.'ur 



:n;ill. <'<|iiiv.ilve<i. moderately convex, oLlong-suLovatc; hinge straight. 



Valre* with a owed ridge on the posterior half or two-third* Tin- ridge may be 

 variiiu-.lv modified. Lut in tin- typical t i- tliin ami Lent like a horseshoe, in 



another tlu> anterior arm is In.ri/.ontal instead (if vertical, while in a third the tun 

 arms arc <livi<led. Kdges simple or faintly Lordered. 



Type: J. crtpidifontit I'lrieh. 



vi-nira! irapace of Jontteli: n,,u 



I'lri.-h; ./, l.-ft ill alKnit x y>. Both S^M-I.-.S an- fr..m th,. I..W.T U-dxpf lh.- 



ruiiiti Knuipa! ..-ky. 



The atlinities of this genus, which includes so far as known only Lower Silurian 

 species, appear to be with linllin, Jones and IIoll. But the horseshoe ridge in all 

 true species of that genus is suhcentral, while the edges of the valves are thickened 

 into a more or less well-developed marginal ridge, no trace of which is apparent in 

 Jones* lln. The new species aboot to be described is peculiar in the faint develop- 

 ment of the loop, and in the shortness of the horseshoe. In ./. ct mix, as may 

 be seen in the aliove cut, the ridge takes up the greater part of the posterior half. 

 Still, a general agreement of part- Let \\cen the t\\o -|..-cic- i- oLvion>. M. that ./. 



<rn may well le a a.s an incii>ient ./.<;/,.>,//</. ( >n the other hand, the 



prominent upper e\t remit ies of the Lent ridge, remind consideraLly of certain species 

 of 1'lrii-hin, Lut as the whole carapace recalls /;///,/ .puite as nuicli. if not more, it i- 

 to be assumed that these resemblances indicate family relation-hip rather than 



ric, A- ii-ual with early types ,,f life, the Lower Silurian Ostracoda are apt to 

 be of a composite nature, and the determination of the really significant features of 

 -uch forms, so far as generic and specific alliances are concerned, is never certain 

 except through minute genealogical in lint this touches upon too large 



a subject for the present work. 



In the original work on the genus I included a Minnesota species, under the name 

 of J. crassa, that I shall now place elsewhere, because it seems to belong to another 

 line of development, namely, it is closely related to Ctenobolbina r'ulmif.i. Cor 

 further remarks on this and related species see under Ctenobn>in<i. 



