17 
PRODUCTUS horridus. 
TAB. CCCXIX.— Fig. 1. 
Spec. Char. Quadrangular, with a large fur- 
row along the middle, eared, thorny; ears 
prominent, sub cylindrical ; beak much in- 
curved, large. 
JL he spines are scattered all over the surface upon ob- 
scure ridges, are large and rather numerous, those upon 
the ears are placed in rows and are particularly strong : 
the surface of the larger valve is so much curved, that 
the ears appear to project from the middle of the sides ; 
they are rather large, convex above and concave beneath ; 
both sides have spines ; the lesser valve is very concave. 
Not very rare in Derbyshire, communicated by Mr. 
White Watson, from the seventh bed of his first Lime- 
stone, probably Magnesian, as it is above the Coal 
series. 
PRODUCTUS sulcatus. 
TAB. CCCXIX. — Fig. 2. 
Spec. Char. Semicylindrical, short, convex 
above, with a concave space along the 
middle; spinose? coarsely sulcated ; hinge 
line as long as the shell is wide. 
The concave space along the middle, and the distance 
of the furrows from each other, distinguish this from 
