60 M ALONE JURASSIC FORMATION OF TEXAS. [bull. 266. 
the plicules separated by striae; preiireal surface ornamented with two 
sets of ribs, of which the anterior ribs are acute, upwardly-imbricate, 
remote, subhorizontal, with gentle sigmoid flexure, presenting a slight 
upward convexity below the beaks and a downward one farther for- 
ward, and alternately reach the more anterior ribs of the other set; 
posterior ribs thicker, more obtuse, and more narrowly intervaled 
than the anterior, nearly straight, and directed steeply downward and 
backward from the limiting angle of the area, the proximal of these 
being the more nearly vertical and the distal and independent ones 
more oblique, the intermediate ones being the longest. Slight irregu- 
larities sometimes appear in the course of the anterior ribs, each of 
which, in one example, bears a small dorsally directed angle at the 
summit of its infraumbonal convexity. 
Measurements. — One of the Texan examples, which has a length 
of 58 mm., indicates for the shell in part restored, a height of 32 mm. 
and a breadth of 23 mm., approximately. 
Occurrence. — The Malone formation yields this fossil rather spar- 
ingly. Eleven specimens and characteristic fragments are repre- 
sented. Eight of these are from the Malone Hills, 1 \ miles east of 
Malone station; the others were collected about a mile east of Kinlay 
station. 
In the character of the preiireal ornamentation, the species pre- 
sent- considerable resemblance to Trigonia snl<<if<iri<t Lamarck, as 
figured by Lycett on Pis. XXVI and XXVIII of his British Fossil 
Trigonia*, a species which has been referred to the Undulatse, but is 
shown by Lycett to belong to the Scabrae. The plain escutcheon! 
however, at once separates T. <<il<l<r<>ni from the Scabrse, and the 
same and all of the other external characters refer it to the Lndu- 
latse. 
Trigonia proscabra sp. n. 
Pi. x. figs. :\-(>. 
Shell small, crescentic-ovate or subsemi circular, the upper border 
strongly excavated, anteriorly inflated, gradually becoming more 
compressed toward the posterior extremity; beaks somewhat pro- 
duced and recurved; escutcheon large, broader than the area, ornaj 
mented with rather remote, coarse, but not \^vy strongly elevated, 
oblique costella); area flattened, narrow, transversely linear plicate, 
traversed by a mesial depressed line, and bounded both above and 
below by a row of tubercles, those of the lower row surmounting a 
distinct limiting ridge and larger than those of the preiireal costs] 
opposite whose terminations they are placed; the area! plications, 
though hue and numerous, are mostly separated by intervals wider 
than themselves; preiireal surface denticulate-costate, the denticles 
