[1903. Whiteaves — A New Species of Matheria. 33 



nearly related to Cyrtodonta and Vanuxemia, and is now included 

 in the family Cyrtodontidce, Ulrich, of the order Prionodesmacea, 

 Dall. The types of M. tcner, which were collected by Mr. J. 

 Richardson and Dr. R. Bell in 1857, at Blue Point, on Lake St. 

 John, are still in the Museum of the Geological Survey. 



A second species of this genus, from the Trenton shales of 

 Minnesota, was described by Mr. Ulrich in 1892, under the name 

 M. rugosa, in the Nineteenth Annual Report of the Geological and 

 Natural History Survey of Minnesota. And, in his Report on the 

 Lower Silurian Lamellibranchiata of Minnesota, published in 1897, 

 in volume three, part two, of the Final Report on the Geology of 

 Minnesota, Mr. Ulrich expresses the opinion that the Modiolopsis 

 recta of Hall, from the Niagara limestone of Wisconsin and 

 Illinois, is also a Matheria. 



In the Museum of the Geological Survey there are a few 

 specimens of a fourth and previously undescribed as well as un- 

 figured species of this genus, from the Trenton limestone of 

 Ottawa, collected many years ago by E. Billings and labelled by 

 him with the manuscript name Matheria brevis. This species may 

 now be defined and characterized as follows. 



Matheria previs. 



/«. 



Matheria brevis. — Figr. i. Side view of the most perfect specimen col- 

 lected, in outline, and showing the marginal con- 

 tour of the right valve. 



Fig. \a. The same specimen, as seen from above, 

 to show the amount of convexity of the closed 

 valves. 



Both of these figures are of the natural size. 



Shell small, inflated and regularly convex, but not quite as 

 wide as high, suboval or oblong subquadrate, about one-third 

 long^er than high and very inequilateral. Anterior side very short, 



