40 MALONE JUKASSTC FOKMATION OF TEXAS. [bull. 266. 
medium sizes at least, the left valve is often ornamented with fine, 
radiating raised lines, including more conspicuous ones, which are 
rather remote, and numerous closely arranged, almost microscopically 
fine ones, there being usually 2 to 7 of the latter in each of the] 
intervals between the former. This ornamentation is usually well 
expressed in very young examples, and these present considerable 
resemblance in form as well as sculpture to certain species of Plica- 
tula, but in the arched valve, held beak upward and seen in exterior 
view, the longer side will appear on the right in the young Gryphsea 
and on the left in Plicatula, since the arched valve is the left in 
Grypluea and the right in Plicatula and the posterior side of the! 
shell is longer than the anterior in both genera. Avery similar orna- 1 
mentation is seen on the arched valve of Meek and Hayden's Blacl 
Hills Jurassic form, Gryphcea calceola var. nebrascensis. In excep- 
tional specimens, G. mexicana approaches the latter species in form 
also, tending to a uniform antero-posterior convexity, even the poste- 
rior flattening being slight. Much more common than this, however, 
is the occurrence of specimens with anterior and posterior sides both 
strongly flattened or concave. 
Measurements. — Specimens of an ordinary size give height, 43 mm.; 
length. 32 mm.; breadth. IT mm.; but considerably larger specimens 
are often found. 
Occurrence. — Common at several levels below the Iota congloiner-' 
ates, a mile and a half east of Malone station, where scores were 
collected, and less so a few feet above similar conglomerates h 
:m anticline in the east flank of Malone Mountain; in the lattei 
locality associated with Pleuromya inconstans, Modiola malonianak 
Astarte malonensis, Exogyra subplicifera? and Serpula <j<>r<]'/<t!is. 
The species was also collected by Doctor Stanton, both at these and 
the following localities; About a mile east of Finlav station; wes 
side of Malone Mountain, west ajid also south of west from MaloiK 
station (at the last-named locality in Nos. 13 and 25 of his Maloi 
Mountain section) ; from foothills west of Malone Mountain, about 
miles north of its southern end; at the west base of the mountaii 
near its southern end; and from the east slope of the mountain, neai 
its southern end, 200 or 300 ( ?) feet above the gypsum. 
One of the most striking features of G. mexicana is the posterioj 
flattening of the left valve, a feature of which is much more strongl] 
expressed in this shell than in any other species of Grypha'a with 
which I am acquainted. 
The prevailing size of the shell is not the same at all localities, 
some specimens of the largest average size coming from the west side 
of Malone Mountain; but at no locality in the Malone district does the 
shell average so small as the Oaxaca examples figured by Doctor 
Felix. 
