in.] DESCRIPTIONS OF SPECIES. 57 
Measurements. — Approximately, height, 7G mm.; length, 87 mm.; 
breadth, 50 mm. Two very young examples have these dimensions, 
respectively, 1G, 17, 10, and 25, 27, 15 mm. 
Occurrence. — So far as the collections show, this Trigonia does not 
occur in the Malone district, except in the Malone Hills and in the 
Theta subdivision of the Trio section. In these, however, 1J miles 
east of Malone station, it becomes numerically one of the commonest 
fossils of the Malone formation. In the rich collecting tract there, 
on the basal slopes of the Truncate mound and the southeast base of 
hill of the Trio, and especially on the western basal slope of the 
former, it was found by scores, in one or two places being agglomer- 
ated in beds, mingled more or less with other fossils. Between 75 
nd 100 specimens of it are represented from this tract. But if the 
shells of other Malone fossils, as here preserved, prove fragile under 
the rigorous temperature changes of a plateau climate, that of Tri- 
gonia vyschetzkU is so especially, and of the large number collected 
many are in half-released fragments, and comparatively few make 
even tolerably fair cabinet specimens. I also found this fossil about 
lalf a mile west-northwest of this locality on the south side of the flat 
saddle that separates the Trio from the low gypsum-parted ridge 
which continues the hill range in that direction. 
The series of quadrate pits mentioned by Lycett a and cited by 
teinmann h as occurring posteriorly on the interior of the valve near 
lie ventral margin in Quadratse, is lacking in T. vyschetzkU. The 
form dingers from that of the Quadratae and agrees with that of the 
lavellatae in being considerably longer than high, yet agrees with 
Juadratae and differs from Clavellatae in being quadrilateral instead 
)f subtriangular. In having the escutcheon ornamented and in 
iome — usually slight — tendency which the areal folds manifest to 
nfringe on the general surface below the limiting angle, on the pos- 
erior region, the shell agrees with the Quadratse. 
The T. vyschetzkU is thus seen to be closely related to the South 
American T. transitoria Steinm., upon which and the related T . her- 
ogi Hausmann, of South Africa, Steinmann, in 1882, proposed to add 
u se\ido-Qu<t<}f<tt<\ c to the previously known sections of Trigonia. Its 
profile is usually less elongate and the ornamentation, especially that 
)f the area and escutcheon, less coarse than in T. transitoria, the 
bids of the area descending the lower slope of the limiting angle, but 
lescending only a little (sometimes not at all) below it on the pos- 
erior region. 
Normal casts of Trigonia vyschetzkU are differently proportioned 
Torn that which — from Tlaxiaco, Mexico — Doctor Felix figures as 
" Mon. Brit. Foss. Trigon., p. 100. 
6 Nenes Jahrb. fur Mineral., 1882, vol. 1, p. 
c Loc. cit., pp. 219-228, Pis. VII-IX. 
