S..L. Penfield—Tiemannite and Metacinnabarite. 449 
it may be observed that while only one imperfect valve was 
collected in Alliford Bay, yet several perfect specimens of both 
valves were obtained at Mand Island. In the writer's judg- 
ment the least that can be said of the whole of the specimens 
collected by Dr. Dawson is that they agree perfectly with 
eek’s description and figure of Pteréa or Oxytoma mucronata. 
8. Camplonectes extenuatus Meek and Hayden. The lower 
valve of a small Pecten from-Maud-Island which was some- 
what doubtfully identified with this species is quite perfect in 
marginal outline, has most of the test preserved, with its char- 
acteristic sculpture, and shows the shape of both ears. An 
upper valve, from the [tasyouco River, corresponds remarkably 
well with Meek’s figure of the type of C extenuatus. 
%. Gryphaea Nebrascensis Meek and Hayden. Dr. White 
Says that the specimens, regarded by the writer as probably 
identical with this species, are more like Gryphaea navia Con- 
ra The irregular, radiating striz on the umbonal region 
which are characteristic of G. Nebrascensis, and which are well 
seen on specimens from the Queen Charlotte Islands and from 
the Iltasyouco River, are altogether absent in @. navia, which 
latter shell has also a narrowly subtrigonal outline with angu- 
lated beaks and a sharp umbonal ridge, a combination of char- 
acters which is not seen in G. Nebrascensis, nor on any of the 
Specimens collected by Dr. G. M. Dawson. 
Art. LVII.—Crystallized Tiemannite and Metacinnabarite ; 
y SaMvEL L. PENFIELD. 
1. TIEMANNITE. 
IN October last, Professor J. E. Clayton, president of the 
Salt Lake Mining Institute, sent to Prof. G. J. Brush a few 
Specimens containing crystals of a selenide of mereury which 
were suitable both for analysis and measurement. The speci- 
mens were from Marysvale, Southern Utah, the same locality 
which afforded the sulpho-selenide of mercury, onofrite,* de- 
Scribed by Professor Brush. A description of the occurrence 
of the mineral, as stated by Prof. Clayton, is given at the end 
of this article, and I take great pleasure in here expressing to 
fim my thanks for calling our attention to these most interest- 
Ing crystals. 
The crystals are black, with high metallic lustre and black 
Streak; hardness about 3; specific gravity taken twice on a 
chemical balance 8°188-8°187; fracture conchoidal; very 
brittle and with no apparent cleavage. 
* This Journal, III, xxi, 312. 
