117 
SPIRIFER trigonalis. 
TAB. CCLXY. 
Syn. Anomites trigonalis, Martin Petr. Derb t 
Tabl 36, f. L 
Sp. Char. Gibbose, transversely striated * with 
26 radiating sulci ; hinge line as long as the 
shell is wide ; front semicircular ; the three 
central ridges elevated ; beaks incurved ap- 
proximated. 
.A lthough this is named trigonalis, the front is so 
round that it can hardly be called even obtusely angular ; 
the spaces between the sulci are rounded ; three of them 
occupy the elevated part of the lesser or upper valve, 
and these are again obscurely divided,. the central one into 
three and the others into two; the flat back meets the 
sides at an acute angle, it is striated ; the whole surface 
is regularly and finely striated transversely ; the stria? 
are elevated and sharp, but often are worn down or ad- 
here to the stone the shell is imbedded in. 
The first specimen of this shell in which I discovered 
the internal spiral appendages was imbedded in a mass of 
Chert that was presented to me by the most eminent 
friend to science Sir J. Banks^ upon whose estate at 
Overton near Ashover, Derbyshire, it was found in the 
Mountain Limestone ; I have confounded it with Anomia 
striata of Martin in my paper in the Linnean Transac- 
tions, vol. XII, part 2, p. 516. The shell is lined, and 
the spiral contents coated with minute crystals of 
Quartz. Within the last two years many specimens of 
