Nezv Species and .Yew Slyuclural Parts of Fossils. 79 



SOME NEW vSPECIICvS AND NEW STRUCTURAL 

 PARTS OF FOSSILS. 



By S. a. Miij.KK AND Charlies Fahkk. 



(Read Auj^ust 2, 1892.) 



MoniOKoi'Sis cokkuc;ata, n. sp. 



Plate /, Fig- 1, left side view, natural size. 



Shell above medium size, oblong, widening behind the beaks, 

 both on the cardinal and basal lines; height a little more than 

 the thickness ; truncated at an angle of nearly forty-five 

 degrees in front of the beaks, and rounded into the basal mar- 

 gin ; posterior end rounded. Basal margin very slightly con- 

 tracted by a shallow undefined cincture that arises below and 

 in front of the beak on each valve and extends obliquely to 

 the basal margin. vSoniewhat winged on the cardinal line 

 posterior to the middle of the shell. Beaks at the anterior 

 end of the shell and extending quite beyond the hinge line. 

 Umbones moderately large ; umbonal ridge swelling in the 

 middle of the shell and fading away toward the postero-basal 

 margin. Surface marked by strong ribs, that originate on the 

 hinge line and at an undefined depression above the umbonal 

 ridge and curve backward and downward to the base, where 

 they are most strongly defined. The posterior cardinal wing 

 is ribbed in- straight and also in slightly curving lines, directed 

 upward and backward from the same undefined depression. 

 A few obscure shallow concentric depressions are seen on 

 some of the casts. The muscular impression is not deep or 

 large, and it is located below and anterior to the beaks. Ex- 

 ternal shell unknown. 



This species is distinguished by the general form, and by 

 the posterior cardinal wing, from M. plwladiformis, which the 

 .surface markings of the .shell would, otherwise, seem to all}' it. 

 It need not be compared with any other defined species. 



