C iRBOVl I i: i:ors .\ E. 23 



(Inc. i.l> ( -nrc, reeular, closely set radiating strlv, about one hundred and Hfly of which may b counted around the 

 .> l.-n- fi.-l.i or mil.- of ti.i-m in-fiipy the |ce of one line. 



Larger or dental valve deprur<l, having usually a broad, very shallow undefined mesial depression extending 

 from tin- fiont toward* the Iwak ; cardinal margin armed with from eii;ht to twelre oblique spines on each side of 

 tli.- I .-.ik ; area of moderate l.r.-.i.lth ; deltoid a]MTtur very broad snbtriangular, the upper angle being rounded 

 aixl the margin) more or leas projecting; impressions of cardinal munle tubovate, diverging, attenuate above; 

 allii t..r mus.-iilar Hears small, narrow, snbelliptical ; mesial ridge small, slight!/ prominent, and scarcely ever 

 reaching the im>l<lle of the valve. 



l''.r-.-il or smaller valve following nearly the curve of the other; beak and central region concave; ears flat ; area 

 well developed but narrower than that of the other valve, provided with menial prominence, which, together with 

 tin' -mall bifld cardinal process projecting from its inner side, nearly or quite closes the foramen of the opposite valve. 

 r'r.'in the hase of thin process there are extending on the inside of the valve five radiating ridges, two of which pass 

 i.l.li.|ii.-ly oiitw.u.N alontf th inner margins of the dental pits, while a third extends at right angles to the binge a 

 little nii'i.- t h.m half way across towards the front of the valve ; the other two ridges are much shorter and occupy 

 intiTiiieiliatH positions between the central and lateral ridges, and are directed obliquely outward and forward. 

 Interior of both valves more or less grannlote, the larger grannies being arranged over a semicircular belt a little 

 within the honliT, which latter is occupied by very fine radiating granulose stria. 



Length, o.t;.' inch ; breadth on hinge line, 1.13 in.-h. 



This shell is \ ( TV closely Allied to f'/nii,,t' \;/< ///,/; of Norwood & Prattcn, and 

 may ])ossihl\ prove to be only a variety of that species. It differs, however, in 

 being generally much larger, rather more compressed, and proportionally longer on 

 tin- hinge line; its ear- are also often much more extended and pointed than those 

 of i'. SinitliH. Another difference is that the coarser granules of the interior seem 

 never to be scattered over the central region of the valves as in Norwood & Pratten's 

 speeiev Again, the area of is -mailer valve ranges more nearly at right angles to 

 the plane of the shell than in Illinois species. 



Lof<i/i/i/ nnd position. Near Fort Ililey, Kansas Territory. Coal Measures. 

 (Type 1066.) 



FAMILY STROPHOMENID^. 



Shell attached or free ; valves both convex, or one convex and the other 

 flat or concave ; hinge line straight, and provided with an area, which is 

 common to both valves, but usually wider in the ventral than the dorsal 

 valve : arms without calcified supports, being probably fleshy and spirally 

 coiled ; shell structure fibrous only, or fibro-punctate. 



Animal unknown. 



This family includes Orthis, Hemipronites, Klitambonites, Strophomena, Leptcena 

 and Tr<>i>i<l<>lt I'fiu. Some authors also include in it the genera Chonetes and 

 Porambonites, but, as Mr. Davidson has demonstrated, the former belongs to the 

 Productidff ; while the affinities of the latter remain somewhat doubtful. 



This group presents one of the many interesting examples in the fossil world, of 

 an entire family, embracing several genera, and a great number of species, which, 

 after existing for immense periods of time, became entirely extinct, long before the 

 dawn of the present epoch. It is mainly a Pala?ozoic family, since it appeared 

 almost with the beginning of life, and became wholly extinct at the close of the 

 Permian period, excepting the genus /.</>/" mi, which continued to be represented 

 by a few species until about the close of the Liassic period. 



