"1'A. 



thick, in a ventral view resembling lip-: surface nf valves gently convex within the 

 \side concave border. the central part nf the upp-'r lialf depre>-ed around a narrow 

 pit; in famt Of the pit OOOftttOnally ft digitl roundel elevation. Surf mtifiilly 



marked witli small pits closely arran^ed-in concentric line-;, usually le- curved than 

 the ventral outline of the valves. 



This is one of the prettiest of the niimerou- i Mracoda occurring in the Trenton 

 of Minnesota. It i- al-o one of the mo-t easily n ..... ^ni/.ed. the thick, lip-like . 

 aii-1 the concentric .surface markings being unusually distinctive. 



tlity. N ;i shales. Goodhiif county, Minm-sota. 



in I'.KYKIciiiA. McCoy. 



Beyr* ""' P- 6 7- 



Carapace small, e.|iiivalved. oblong or semiovate, with a straight dorsal and 

 convex ventnil outline. Typically each valve has twosulci and three lobes, of which 

 the- cent nil one is the smallest ; the- two larger lobes often coalesce ventrally. Surface 

 u-iially marked witli pittings, reticulation, papill.f or other ornament. 



Type: /.'//////; /'i M.-i'oy. 



This genus, after /;. i- the mo>t important of all the generic groups of 



1'aleozoic Ostracoda. Many of the species also, those of the Upper Silurian rocks 

 especially, are comparatively large, specimens over 3 mm. in length being not at all 

 uncommon. The individuals, moreover, are generally abundant, layers of rock in 

 many instances being crowded with, if indeed they are not largely made up of their 

 -eparated valves. 



In the restricted en-e in which the genus is here defined, the oldest known 

 species is the Minnesota form about to l>e described.* It i- from the middle third of 

 the Trenton shale- ( M'.lack River ^roupi. <>f the Trenton proper. /'. Mia Walcott. 

 m. iv belong to the genus, and I have a doubtful species from the I'tica hori/.on .it 

 Cincinnati. Ohio; but so far we know of no true Hei/ri<-lii,i from the Hudson Kiveror 

 Cincinnati ^roiip. tln^e referred to the ^enu- from this formation belonging to 

 ;./. l>rri.-inrll,i. Unlit-' ' ///. ++rn+rU,, and / 'rimifi.i. In (lie ( 'linton. 



however. It. luta Hall iVanuxei .1 good s| ,md from here on to the close 



of the Carboniferous system the genu- i- more or le-> well rcpre.-cnted in e 

 group of -trata. 



Prof. T. Rupert J.mp. bu dracrllMd n^rlrkla Mil from the Mlna-vln fliun of Urvil Britain . ii.-.,l MM., n -T . DM. 

 1 vol. 8. p. JO:1IV t>ut tin- afflnlllraor thp foMll wln to luc ..!-.., Mf.,1. 



s li.Jlla lota J<wr, im. VJuart. J.iur. O.! t*. p. II, pi. a. fljr>. I. !. 3. The peclmvno Idrnllllf 



Joom with II. lain ar* wldflj ilHT.-r.-nt frvm the lypk-l ( : K ipcvfea. which I. a Irur flryrfeTifci. l.ul I 



rannoi >1 hru from Bultla fymmrtHca Rail, ap. 



M 



