188 rONTRIBUTIONS TO rANADIAN rAL-T,ONT0Lr)OY. 



Thunder Hill, Township 35, Eange 30 W., three specimens, D. B. 

 Dowling, 1887. All from the Niobrara group, or upper part of the 

 series. 



The specimens collected at these localities are usually little more 

 than imperfect casts of the interior of detached valves, but they repre- 

 sent the typical form of the species rather than the variety aviculoides 

 of Meek and Ilayden. 



On account of its real or supposed eai-lior date, a question which the 

 present writer has no means of investigating, the name /. labiatiis is 

 preferred to I. prohlematicus by Stoliczka and some other German 

 palfeontologists. 



MODIOLA TENUISOULPTA. (N. Sp. ?) 



Plate L'6, fiKS. L' and 2a. 



Shell elongated, compressed, the length being more than twice the 

 height, and the greatest thickness through the closed valves about one- 

 third less than their maximum height ; umbonal slopes rounded, nearly 

 obsolete, and not at all angulated. Superior border moderately elevated 

 and somewhat angular a little behind the middle ; hinge line straight, 

 occupying rather more than one-half of the entire length, and forming 

 a very obtusely subangular junction with the obliquely convex down- 

 ward slope of the anal mai-gin ; postoro-basal extremity rather 

 nari'owly rounded ; basal margin shallowly concave ; anterior extremity 

 forming a subangular, but somewhat I'ounded, nari'ow lobe which 

 projects a short distance bej'ond the beaks, the latter being small, 

 depressed and appressed, with a forward inclination. 



Surface marked by fine and very numerous i-adiating ribs, which 

 bifurcate at irregular intervals, and which are crossed by extremely 

 minute concentric striic, as well as by a few distant and impressed 

 periodic arrests of growth. The radiating ribs are coarser above the 

 nearly obsolete umbonal slopes than they are below them, and the 

 concentric striffi which ci'oss them are too small to be visible without 

 the use of a lens. 



Characters of the interior of the valves unknown. 



Dimensions of the most perfect specimen collected : maximum 

 length, fifty-three millimetres; greatest height, twenty-two mm.; 

 breadth or thickness, fourteen. 



Swan Eiver, Township 37, Range 26 W., J. B. Tyrrell, 1887: a 

 somewhat imperfect cast of the interioi- of the closed valves, with a 

 small ])ortion of the test |ireservcd, and a well pi'escrved portion of 

 lb(^ mould ol a detached valve. K'ojling River, Township .'!.'), Range 



