GENERA PRODUCTUS AND STROPHALOSIA. 
147 
while the disposition of the reniform vascular impressions of the dorsal 
valve is a distinctive feature. 
In reference to the Genus Productus, Mr. Davidson remarks as fol¬ 
lows : 
“ All well authenticated species of Productus, hitherto examined, have shown 
“themselves to be edentulous; but whether this character was general and 
“ without exception, may remain a question for further consideration : anyhow, 
“ the dorsal valve must have turned on its hinge-line with as much precision as 
“ in Chonetes, which possessed regularly articulating teeth. It has been often 
“ asserted and believed that Productus might be distinguished from its subgenera 
“ by the total absence of an area; and although this is the prevalent character 
<£ of the genus, still in certain species, such as P. sinuatus, a perfectly developed 
“ area is generally present in the ventral valve. There exists also an occasional 
tl tendency to the formation of hinge-area in several species; as may be seen, for 
“ example, in the remarkable example of P. semireticulatus , of which a repre- 
“ sentation is given in Plate xliii, fig. 5.”* 
These observations of Mr. Davidson are of later date than his “ Intro¬ 
duction to the Natural History of the Brachiopoda.” 
One of the important features of distinction between Productus and 
Strophalosia has been stated to bo the different disposition of the reni¬ 
form vascular impressions in the dorsal valve. The accompanying figures 
represent this character in two species of the latter genus, as given by 
Mr. Davidson in his Introduction. 
In examining the species occurring in the higher formations of the New 
York rocks, which I had supposed might be referred to the Genus Stropha- 
Monograph of British Carboniferous Brachiopoda, p. 136. 1861. 
