G. B. Grant on a new Difference Engine. 113 
and in front of the umbones, instead of being straight and sud- 
enly curved downward, is regularly rounded as in E. Dunkeri. 
Behind the umbones the shell is narrower than either in Cald- 
welli or Dunkeri; the dorsal edge sloping rapidly downward, 
without the well marked angle of Caldwell, or the continuous, 
curve of Dunkeri. Coarse punctures between the ribs, 
rather coarser than in Caldwelli, there being on an average 
between the ribs in the center of the valve. Length 50; 
th ‘33 ; thickness -24 inch. Six specimens from Dubuque, 
Towa, collected by Rev. A. B. Kendig. Dedicated to Prof. 
E. S. Morse, who ‘has indicated to me that the species was un- 
described, 
Lymnetis gracilcornis, n. sp.—This interesting form may at 
Once be known from L. Gouldiz Baird, recently found by Mr. E. 
the front edge, while in Gouldi it does. Shell of the same 
form but much larger than in Gouldiz. Length of shell 17, 
breadth -16 inch. 
Peabody Academy of Science, Salem, Mass., May 20, 1871. 
Ant. XV.—On a New Difference Engine; by Guo. B. Grant. 
THE great labor and expense involved in the construction of 
teliable astronomical and veaeial tables by mental computa- 
i mee . . 
| he English government appropriated eighty-five 
AM. Jour S$ct—Tutrp Serres, Vor. II, No. 8—Aveust, 1971. 
8 
