36 MALONE JURASSIC FORMATION OF TEXAS. [bull. L»G6. 
SPATANCxOIDA. 
Genus PYGURUS Agassiz. 
Pygurus sp. 
Among- the specimens submitted by Doctor Stanton is a fragment of J 
the test of a sea-urchin of the genus Pygurus. It includes the main! 
part of the aboral half of an ambulacrum. The genus is clearly 
determined by the form of the ambulacrum and (he form and arrange-j 
meiit of the pores, as well as by the character of the tubercles and by 
the discoidal form of the test, the latter form being indicated by the 
flatness of the part preserved. The ambulacrum has the biconcave 
outline that characterizes the upper part of that of Pygurus. The^ 
pores of the outer row are very long and slit-like, widened slightly 
toward the outer end. and subhorizontal to more or less oblique; those] 1 ) 
of the inner row more ringent, compressed dot-like or hyphen-like 
and oblique, their width being considerably less and their length con- 
siderably more than that of any of the circumt ubercular courts on the 
neighboring part of the ambulacrum. The ambulacra! plates are 
exceedingly narrow: the imperforate pari of each, in the widest part 
of the ambulacrum, being about ten times as long (transverse) as 
wide (parallel to the course of the ambulacrum) and ornainente(j 
with 1 to 3 small perforated tubercles, each of which is set in a round 
depressed court. The distribution of these tubercles is irregular, but 
they are so few and so feebly developed on the inner ends of thl 
plates as to give the ambulacrum the aspect of having a median plain 
/one. to which the seams between the plates give a transversely stri 
a ted appearance. 
Measurements. — Maximum width of amb.ula.crum L6, of which the; 
two pore belts each occupy 3.5 and the imperforate tract 9 mm.; 
length and width of imperforate pail of an ambulacral plate in 
broadest part of ambulacrum, respectively. 1.5 and 0.43 mm.; length 
of outer slit-like pores in broadest part of ambulacrum 2 mm., which 
is about one-fourth of the width of a seniiambulacrum. 
Occurrence. — West side of Malone Mountain, about 2 miles south- 
west of Malone station, in No. 25 of Doctor Stanton's Malone Moun- 
tain section; with Gryphcea mexicana, Pleuromya inconstant. Pinna 
guadrifrons, etc. 
