LAMKI.I.IIiKAV 111 s >7 



KMODONTA nNHH>l;VI". n. 



*. n-m. 



shell small, compressed convex, transrenely somewhat a uminate-ovate. tapering 

 riorly to a narrow!} rounded extremity; anterior end shorter than the postf 

 hut iniich higher and broadly rounded, except in the autero-cardinal region, where 

 the outline projects slightly beyond the path of a uniform curve; base rather prom- 

 inently rounded in the middle, convex throughout the anterior half, straight or very 

 faintly -innate in the posterior half; beaks small, not prominent, situated about 4 mm. 

 Miin.l the anterior extremity in a specimen 1 1 nun. long; posteriorly from the beaks 

 the cardinal outline is straight, in front of them gently concave. Ilehind the center 

 the shell is more or less distinctly contracted. Surface with obscure concentric M 

 Hinge plate of moderate strength, comparatively long, very gently bent, and just 

 appreciably contracted beneath the beaks, with about twenty-seven nearly vertical 

 teeth in each valve, twelve in front of the beak. The posterior six or seven teeth are 

 stronger than the rest and bent inward. Test thin, muscular scars not observed. The 

 largest -penmen seen, a right valve, i- 1'J nun. lung. 7.1 nun. high ami l.s mm. thick. 

 The contraction and narrowness of the posterior end gives to this species some- 

 what the appearance of C. contrnrtn Salter, but the two species are really widely 

 ditlerent. The Canadian shell is higher, more convex and its cardinal outline much 

 more angular, the hinge plate strongly bent and very narrow under the beaks, the 

 teeth larger and not so numerous, and the shell much thicker. The affinities of 

 C. cuneiform is are probably with C'. nasuta and C. subnnsutn. The former, being a 

 much larger shell, is not likely to be confounded with it. The latter is narrower 

 anteriorly and wider posteriorly, is more convex, especially in a front view, its 

 posterior half is not contracted in the same manner, and the anterior outline more 

 uniformly rounded. 



tation and locality. Four -irnii.n> were found at point about fix mile* south of Cannon 

 Falls, Minnesota, wln-n- ttu-y ocourn-d In the upper part <>f th<- middle thin) of th.- Trenton Khali*. The 

 same locality and bed has furnished numerous nth.-r Lamelllbranrhlata. 



gibbtruln section. 



\ I.IIIBM. '//-. 



I-I.ATF. xi.n m; r 



i trnodonta gibberula SAI.TKI:. IH57. Canadian Organic I)- i. p. 38. 



T'llinomfa rentrieota Hu.i.. II. Itep. Supt. Geol. Sur. WI-, ],. 27: Ivi- Final K.-p..rt of um, 



p. 38, fig. 3; MKKK and Wuici HKN. ISJ8, Owl. Sur. 111., . *r.. 



Shell rhombic subovate. ventricose, the bight, length and thickness, reap- 

 as seven, ten and -iv. with large incurved l>eaks. situated a little behind the mid- 

 length; antero-dorsal and ventral margins subparallel, the posterior end oblii| 



