76 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 78 



/. longula, and /. suberecia. From the first and second of these allied 

 species it is readily distinguished by its shorter hinge line and corre- 

 spondingly more produced posterior end. The differences are quickly 

 noted in comparing the truncation of the species. For the same 

 reasons the posterior half of the valves appears to be narrower in 

 /. dermatoides. The other two species, /. longula and /. suberecia, 

 differ in the opposite direction. In both the hinge line is even shorter, 

 and when this line is placed horizontally their carapaces appear more 

 erect. The latter difl'erence is best shown by the strong downward 

 trend of the anterior and ventral sides from the horizontal hinge line. 

 A closer relative, perhaps, than any of the named species is indicated 

 in the following /. matthewi. For comparisons see remarks under 

 that species. 



Occurrence. — In thin limestone intercalated in or overlying the 

 Cambrian roofing slate referred to the Lower Cambrian by Doctor 

 Walcott at several localities in Greenwich Township, Washington 

 County, N. Y. A single specimen, injured in front, and therefore 

 somewhat doubtfully referred to the species, is from the "Middle 

 Cambrian" (Clc) at Hastings Cove, Kennebecasis River, 6 miles east 

 of St. John, New Brunswick. Identified by Cobbold in the Lower 

 Cambrian limestone with Strenuella at Comley, England. 



Holotype. ~C&t. No. 17474, U.S.N. M. 



INDIAN.\ MATTHEWI, new species 



Plate 9, Figure 15 



Description. — Carapace small, obliquely subovate, narrowing ante- 

 riorly, hinge line three-fifths of greatest length, postdorsal angle 

 obtuse, sometimes even rounded off, anterior angle sharply defined, 

 almost rectangular; anterior margin scarcely bowed in upper part, 

 the curve from the dorsal angle to the postventral side decreasing 

 very gradually and on the whole gently; posterior margin more 

 strongly convex, with greatest prominence in lower half; upper half 

 oblique, in most instances appreciably straightened. Valves without 

 rim, but the anterior edge, especially of the left valve, is sometimes 

 raised slightly as though to widen the gap between the valves; surface 

 moderately convex, the highest point a little behind the center; a 

 more or less obvious but wide and undefined depression in the dorsal 

 slope. Test light brown or black, smooth and sometimes polished, 

 apparently not punctate. 



Dimensions of largest specimen: Greatest length 4.0 mm., length 

 of hinge line 2.3 mm., greatest height 2.8 mm., thickness (of single 

 valve) about L15 mm. 



Remarks. — In most respects this species occupies an intermediate 

 position between 7. secunda and /. dermatoides. It differs from both 

 in the more rectangular form of the antero-cardinal part of the 



