Fig. 
PLATE XIX. 
1. Strigocephalus Burtini, Defrance. Diagram ofa longitudinal section exhibiting the 
2. Productus giganteus, Aarti 
3. Productus semireticulatus, 
mternal structures: a, ventral median plate ; 6, crural 
base ; ¢, crura of the loop; d, loop; e, cardinal muscular 
fulcrum; 7, situation of the foramen in the area. The 
original specimen is from the Devonian system of the 
Hifel. 
nm. Cast of the large valve, natural size: a, impressions 
of the superior pedicle muscles; 6, ditto of cardinal 
muscles; c, ditto of valvular muscles; d, ditto of the 
veins nourishing the superior pedicle muscles; e, ditto 
of labial appendages. Carboniferous limestone, Lowick, 
Northumberland. 
(The letter e¢, referrmg to the valvular muscular impressions —viz., 
the pair of small ones immediately behind those of the cardinal 
muscles 6—has been inadvertently omitted). 
Martin. Figure (natural size) of the inner surface of 
the flat valve, and the inside of the umbone of the large 
valve; testiferous. The former showing the cardinal 
muscular fulcrum (a); median plate (4) ; impressions 
of the posterior divisions of the valvular muscles (¢) ; 
ditto of the anterior divisions (7); and reniform 
4. Productus giganteus, Mart 
impressions (/). Carboniferous Shale, Redesdale, 
Northumberland. 
n. Diagram of a longitudinal section (left half of the 
shell), exhibiting a restoration of the muscular 
system: a, pedicle mass; ¢, superior pedicle muscle ; 
d, cardial. muscle; e, valvular muscle; 7, cardinal 
muscular fulcrum ; g, inferior pedicle muscle ; 7, dorsal 
median plate; 2, longitudinal section of the large 
valve. | 
(The dotted line connecting the letter a with the pedicle mass 
—i.e., the part in the inside of the umbone—has been unin- 
tentionally omitted). 
“he — = Diagram of a transverse section (looking within the 
umbonal region) exhibiting a restoration of the muscular 
system. 
(The letters in last figure'agree in their references with those of the 
present figure. To prevent confusion, the inferior pedicle 
muscle (g) of last figure is not represented). 
