58 
MALONE JURASSIC FORMATION OF TEXAS. 
[BULL. 260. 
the type of his T. sologureni® a shorter, more elevated, and much 
more ventricose form being indicated for the latter species. But the 
cast of T . vyschetzkii^ in one or two of our specimens, somewhat 
approaches that of T. sologureni in form, while several species of 
fossils are common to Malone and Tlaxiaco; so that it is desirable to 
compare actual shells of these two species with one another as well as 
with the shell of T . transitoria. 
Trtgonia goodelxj] Cragin. 
Pi. x, figs, l, 2. 
Trigonia goodellii Cragin, 1897, Jour. Geol., vol. 5, p. 816. 
She'll of about medium size in its genus, produced ovate, ventricose; 
valves thick ; beaks situated near the rear limit of the anterior fourth, 
low, strongly inflated, in contact, their posterior slope strongly angu] 
iated to form the limiting angle of the area; area flattened, nearly 
plain, having numerous line oblique growth lines, with a few small 
folds crossing it near and concentric to the beaks, these folds beim 
continuous of and making an angle with those in front of the area, 
some low tubercles along the marginal angles, and a faint mesial 
sulcus; escutcheon bearing only inconspicuous folds which radiatj 
from the ligament, those of the proximal part being nearly transverse 
to the length of the escutcheon and continuous with those of the cor-j 
responding part of the area; general ornamentation consisting of 
series of ribs, which on the posterior part of the preareal surfa< 
are large, obtuse, and plain or subtuberculated, separated by round- 
bottomed valleys of about their own width, and descend almost verti-1 
cally (the earlier ones more obliquely forward) from the inferioi 
border of the area, increasing in size each to an elbow-like angle, ai 
which they turn abruptly forward, becoming reduced in size i 
costellse in front of these elbows and partially resolved each into 
series of small tubercles, these costelhe being accompanied each by on( 
or two similar ones in the intervals between them, the costelhe dimii 
ishing gradually in size and swinging into the course 1 of ordinary 
growth lines on the anterior region, and there becoming continuouj 
and like strong reversed imbrications, each presenting its acute anc 
more elevated border dorsad. The series of costal elbows radiates ai 
first downward and then obliquely downward and backward froi 
the beaks. 
M< usiwements. — Height, 42 mm.; length, about 58 to GO (plus? 
mm. ; breadth, 35 mm. 
" Versteinerungen aus dem obereb Jura des Cerro de Titania bei Tlaxiaco iro Stai 
Oaxaoa, L801, Beitr. Geol. u. Pal. Mex., pi. ::, Palaeontographica, vol. 37, p. 17!>, 1' 
XXVI I, figs. 2, 2a. 
