198 
TRIGONIA dedalea. 
TAB. LXXXVIII. 
re 
Srec. Caar. Obtusely rhomboidal, with many ob- 
lique rows of tubercles; anterior side angular, 
with many scattered tubercles, and one longi- 
tudinal row, bounded by a longitudinal ridge, 
on which is another row of large tubercles. 
Syn. Trigonia dedalea. Park. 3, T. 12. F. 6. 
with smaller tubercles. 
or ee 
Neanrty half the surface is occupied by the flatter part, 
which | call the anterior side; from the tuberculated ridge 
which bounds it, the oblique rows of tubercles which cover 
the rest of the shell descend towards the front, except near 
the beak, towards which three or four rows incline; they 
are gently recurved. The scattered tubercles upon the 
flatter part are smaller than the others, and are arranged in 
quincunx order; the length is rather greater than the width. 
There is a variety with smaller and more numerous tuber- 
cles referred to above. 
I feel much pleasure in presenting so complete a speci- 
men of this singular and rare species, through the kindness 
of my friend T. J. L. Baker, Esq. Few specimens have 
good hinges, but here happen to be the two opposite valves 
showing the hinge, which Mr. Baker with much pains 
cleared from the earthy agglutinated particles which ad- 
hered to it, so that it is likely to be the most perfect speci- 
men of the species known. It is siliceous or agatized, and 
semitransparent. I find, by comparing the opposite valves 
and imperfect specimens, that the series of stud-like pro- 
tuberances is sometimes more or less interrupted in regular- 
ity. On the broader side, however, a peculiar arrangement 
is very constant; this may be plainly observed on the left 
hand side of the valve I have pictured. It is that two of 
the rows a little below the apex diverge from each other, 
and form an angle, the space within which is filled up by 
angular sets of tubercles, each like a letter V, placed one 
within another. The irregular size of the tubercles upon 
the other half, and their sometimes passing into each other, 
make the order appear confused. A few single shells have 
been found orderly and distinct, but there will be no doubt 
as to the species. It will be seen that the form of the hinge 
in this Genus is necessarily connected with a thick shell, 
very unlike the Genus Plagiostoma, with which only 
(1 believe) it has been confounded. 
