M KM.! I.KAN. II1ATA. 

 WI.I1.1U oli|l.|UU.) 



of the shell, with two t<> li\f rather olnl.|iie folds ur teeth in front of the beaks. 

 l'o*terior portion of hinge apparently ed.'iitulou*. Ligament proli.ilily l-oth e\t> 

 :iii-l internal, tin- latter only along the posterior t hird of t lie hinge line, win-re it WM 

 supported liy an internal ridge in each valve. Two -implr adductor impre**ion*. t lie 

 posterior 01 r'.iint; pallial lint- simple, marginal; interior of shell lined \\itli a 



nacrous film. Surface nf *|iell wit li tine c<> ncen trie line*, and *oine times with stronger 

 concentric undulation*. 



Ty I './I./M./ I' I rich. 



Ni- more ea>ily re- : -*MIII- of Lamelliliranchiata than tlii- i- known from 



the I.owi'r Silurian rock*, and of those restricted to that system, none i* more 

 important in the way <>f ~pecu-> and 'li>tril>ution. Twelve -pfcic-. nine of them 



ton. the rest from the Hudson Ifivi-r ^roiiji. are de>crit>ed and figured in this 

 work. Two other* wen- dr*crilied hy mo in IS'.KI, from the ( 'incinnati group of Ohio 

 a* II'. itnifn<it(i and 1 1". sitl,->r.if,i. while another pair. Itimii and plrlteiti, from the 

 h'iver roek* of Ant icosta, were douhtfnlly referred by Hilling* to hi* j.'fnn* 

 'i. With the latter - Hillings describes two others as Cyrtmlm 



and f. acutninli<in<i (1 '.il. Sil. Koss. y^nticosti, pp. 1'! and 4'.l). which 



may turn out to lielonj/ to \Vlntrll-i. The ' 'nlitr.s curinata Meek, from Cincin- 



nati, ( >hio. ;il*o lielonj:* here, while a very large species from tlie upper beds of the 

 *ame formation remain* to l>e descril>ed. Species of this genus have been referred to 

 Ihlnhi-'i M. ' frifinlites Conrad, and Cyrtodonta Hillings. McCoy describes hi* 



;.".'n-. tainin^ inei|uivalve shell* in which the binge is edentulous. <' 



and Ciirtuiliintn hoth have well developed posterior lateral teeth and quite different 

 cardinal teeth. In the latter also the shell is thicker and the ligamental area never 

 nor is the umbonal ridge ever so prominent as is commonly the 

 case in Whitelln. 



\\ II1TKI.I.A IMU.IVl! ATA I'll 



PLATE XL. FIOS. 11 and a. 

 \\'hitlla oblin .'< a, ISt. Ani.-r. Gwil., vol. vi. |, 177 



Shell large, oblique, suhrhomhoidal in outline, produced in the postero-basal 

 region, \entrii-ose. with point of greatest convexity above the middle; beaks rather 

 small, prominent. *li^htly incurved. *itnated nearly one-thin I of the length of the 

 hinge line from its anterior extremity: unibonal ridge well marked, the cardinal 

 slope concave Ant nail, narrowly rounded merging gradually 



the evenly and only moderately convex ventral margin. Posterior end sharply 

 curved and produced below, gently convex and slopit;. id in the upper ha 



meet the slightly convex, cardinal margin. K*cutcheon well marked, wide, shallowest 



