il cl lai a a et i | 
Dr. Genth’s Contributions to Mineralogy. 15 
As to bulk, also, the Temperate zone probably has the prepon- 
derance ; yet our data are less definite. In the Galatheidea, the 
cold-water species are not only ten times larger lineally (which 
implies at least eight hundred times cubically), but they are far 
more prolific, swarming in vast numbers where they occur. The 
Thalassinidea are more numerous in extra-torrid species than tor- 
rid, as well as larger in size. The Scyllaride are mainly trop- 
ical ; but the species are not of common occurrence, compared 
with the Astacidz, which abound everywhere, and these, as well 
as the Crangonide and Pandaline, are all ‘T’emperate zone spe- 
cies. The Palemonine and Peneide probably preponderate in 
the tropics, and this may be also true of the Alpheine. Taking 
a general view of the whole, and considering the fact, that the 
extra-torrid species rather outnumber the torrid, we believe that 
the deduction above stated is correct. 
In the T'etradecapoda, the number of species, the inhioe and 
diversity of genera, the number of a and the bulk, are 
all greater in the extra-terrid seas than in the torrid, as has been 
explained on a preceding page ; and this is seein true of the 
Amphipoda. 
The tendency to spinose macs among the species of the colder 
temperate regions, or Frigid zone, has been remarked upon on 
page 9, as exemplified among ne Gammaridea, the Crango- 
hidz, nathoiies, and Maioids. 
(To be continued.) 
Art. III.—Contributions to heed ; by Dr. F. A. Genta 
of Philadelphia. 
(Continued from vol. xviii, p. 410.) 
5. Tetradymite. 
Arrer making the examination of the Tetradymite from Da- 
vidson county, N. C. (Am. Journ., 2d Ser., vol. xvii, page 81), I 
was very desirous to reéxamine ‘the m mineral, which had been 
agi by Mr. Coleman Fisher, Jr., (Am. Jour., 2d gee vol. vii, 
Pp. 282). Fortunately Prof. R. S. McCulloh (who was at the time 
of its discovery at Commodore Stockton’s mines in Virginia, 
Melter and Refiner at the U. S. Mint) had preserved some of 
the same material, which was" analyzed by Mr. Fisher, and he 
very ee gave me all that he had for examination. This was 
sufficient or the whole investigation. ‘The pieces were of two 
sna sis: Tetradymite associated with quartz and gold, 
and Tetradymite in broad folia, sometimes one inch in diam- 
ster, Stnpinted in a decomposed micaceous slate. The latter 
mineral undoubtedly came from the Tellurium Mine, Fluvanna 
: county, Va. and is Hat eoayeed by Mr. Fisher; the former is 
