PLATE XIX. 



Fig. 



1. Strigocephalus Burtini, Def ranee. Diagram of a longitudinal section exhibiting the 



internal structures : a, ventral median plate ; b, crural 

 base ; c, crura of the loop ; d, loop ; e, cardinal muscular 

 fulcrum ; /, situation of the foramen in the area. The 

 original specimen is from the Devonian system of the 

 Eifel. 



2. Productus giganteus, il/«r^«;2. Cast of the large valve, natural size : a, impressions 



of the superior pedicle muscles ; h, 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 c, referring to the valvular muscular impressions —viz., 

 the pair of small ones immediately behind those of the cardinal 

 muscles b — ^has been inadvertently omitted). 



3. Productus semireticulatus, 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 {b) ; impressions 

 of the posterior divisions of the valvular muscles (c) ; 

 ditto of the anterior divisions id-) ; and reniforra 

 impressions (/). Carboniferous Shale, Redesdale, 

 N orthu rab erlan d . 



4. Productus giganteus, Martin. Diagram of a longitudinal section (left half of the 



shell), exhibiting a restoration of the muscular 

 system : a, pedicle mass ; c, superior pedicle muscle ; 

 d, cardinal muscle ; e, valvular muscle ; /, cardinal 

 muscular fulcrum ; ff, inferior pedicle muscle ; j, dorsal 

 median plate ; n, 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). 



5. — — Diagram of a transverse section (looking within the 



umbonal region) exhibiting a restoration of the muscular 

 system. 

 (The letters in last figure"agi-ee in their references with those of the 

 present figure. To prevent confusion, the inferior pedicle 

 muscle (</) of last figure is not represented). 



