1. \M1-.I. l.ll'.l: \\. III A'l \ 



II* 1 



tin- margin i> rounded iu >'. -fi-inliiin. The four or live I 'inciiiii.it i ipecitt kimun to 

 me arc ail much higher p.Meriorly. 



..',"/ \| . i- -ilMHil 



thin- 



U > Ml' 'KI'IA. n. : 



Shell rather -mall, tran-ver-ely -uKovate, in Ay convex. e|iiivalve. 



inequilateral; hack arcuate. Leak- anterior, not large, curving ohli.[iiely inward ami 

 forward; iiinl.oiial ridge moderate; Let ween the ridge and the dorsal edge a m<" 

 !>- distinct Milciiv A -harply detined liinule lieneath the ;i|i|iro\iinate lieaks, while 



i to tin-in tln-ro extend^ to the extremity of tlio hinge an e.jiially <listinct 

 ^iitrhi-on. Millie plate thin, arruate. with one hori/ontal wed^e--ha|.ed cardinal 

 t.x.th in the left valve which entered into a rorre.-poinliiiL' ravity in the under -ide 

 of the hin-e plate of the right \al\e iinniediately behind the l>eak. l'o>terior half 

 of hinge ci.iiM-ting of a slender lateral tooth in the left valve and a corresponding 

 furrow in the right. Anterior to the center an elongate depression for the reception 

 of an internal ligament. Anterior miHcul.ii -car di-tinct. deep, siihcircular. situated 

 heneath the Itinultv. pallial lino simple, siilmiarginal. posterior scar undeterniined 



:ier thick in the anterior part. 

 Tyi ///>. n. -p. 



.de the type, the Hudson Kiver >trata of l-'illmore county. Minnesota, contain 



anotliet having the charactei -ed to this genus. This I puhlisbed 



.1 ni-w -pecie of i '!>< 'iin>i'i. gi\ ing it the specific name siilnn/orsnta. It 



i- a more e; -hell hut otherwise do-ely related to S. ventralis. A third sjiecie-. 



thi- one from the <ialena. I described from ca-ts of the interior ax Cijiir'n;ir<l 



The position of Snii'uriliu seem to ]i.- near the hevonian < innniniixin. the hinge 

 Keing similar in the two genera, though not l>y any means identical. In Unimntijsiu 

 nameh. iown in Hall's work on the K-vonian I.amellihranchiata I I'al. New 



'I ork. vol. v, part i. plate i.vni. tig. (i). there i< no cardinal tooth in the left valve as in 



:ider posterior lateral teeth represented. Another di- 



tingiiishing feature of the latter, and one that is common to many Lower Silurian 

 shelK i- found in the greater depth of the anterior muscular scar. In the genii- 



// the hiiiL'e. a-i'h- from th> e-.-utcl:. (iiite ditlerent. the te~t 



thin, and the muscular impr. .-xi-eedingly faint, while the hack, instead of 



Keing arcuate, i- conc.i\,- I.ehind the lieak-. the latter I.eing aNo tumid and much 

 more prominent. 



