OSTi; IOODA.. 



Prlmlilrlla.) 



cinnati specimen^. Tift lOrflbOO !<> IB MATMly M> OODTQJ iier it i> not thrown 



up into a j.iiiiit n>;ir the center. Init i- comparatively uniform in curvature. 



'ifrrfllil .Jones (Contri. < 'an. Micro-Pal.. pt. iii. p. '._': IV'I) from the 

 <'ha/\ at l.ake Winnipeg. i a clo-eh i. if not identical form. However, as 



figured liy Prof. .lone-, it appear- to he le- \ ami the outline not so prominent 



in tin- po-t -ventral region. 



.in./ i...;iiit-i. Tin- sui:ili ilnrii < f tin- Trenton sbaln near 



Kiiiintaln, ttu- l;irK'-r fnun tin- top of tl, ' nin-sota. 



Family I5KYKICI1III' 

 0101 PKIMI rir.l.!.\. n. -on. 



.ipa<-' ii-ually olilon^. *.|iiiv.ilvt"l. moderately convex; surface smooth or 

 finely pnnctato; in tlio .lor-al slope a broad, shallow and quite undefined depression 

 represents an undeveloped mesial siilniv 



Type: / -/</(. n. sp. 



the four new species about to be described, I propose to place in tln- 

 genus Ijrpcrditia unintrnis I'lrich ( A purr liitrx, I'lrich, I'rimitin. .lones^ and I'rimitin 

 trliU /Mil i .lones, from the lower part of the Cincinnati ^roup. I'/hnitin iilrirhi .(ones, 

 I'tica slate, Canada, and prohalily the Kurnpean species, I'riniHia mutiilinii and 

 rirhiumi .(ones and Holl. I'riinitiu minuln Kichwald (as figured by Jones) and 



'Hi/nin. var. nmlii. .lone~. 1 am inclined to think that Isocliilinn ? fabacea Jones, 

 from the Hamilton of New York, and Apnrchite* inurnutu* I'lrich also should be 

 placed here. These species constitute a very natural group, distinguished from 

 .!////</; /'/-.- liy the dorsal depression. They are separated from Primitia because they 

 give no adequate idea of that most prolific genus. To be a 1'i-hnifin in my eyes the 

 valves must l>e provided with a well marked sulxvntral pit or sulcus. 



The Carboniferous genus }',,/<, md K irk l>y, is closely simulated in all 



respects except the crenulated hinge by I'rimiticllu Innlmtn. Possibly thatgenus is 

 not so far removed from I'rimHiflln as we now believe to be the case. 



PKIMITIH i.i. \ 001 k, . >//. 



K.-ntu<-ky >] '.'' mm.: thlrkn.--. n 24 mm. 



Minnesota 0.60 " " " 1:1 " 







.pare elongate, suliclliptical or >uli[iiatlrate. the length nearly twice the 

 hight, convex; donwil margin long, .-traight. with both extremities angular, or with 

 the anterior one obtuse or rounded; ventral margin nearly parallel with the do: 



