BRACHIOPODA. 387 
Strophomena incurvata. ] 
cardinal area along each side of the chilidium, with the thin, erect, crural plates 
forming their inner walls. The space between the crural plates is slightly thickened 
and occupied by a short, strong, bilobed cardinal process. Its upper surface is trans- 
versely striated and has a shallow median depression along each lobe. The rostral 
thickening is continued forward but a short distance and converges to a low median 
ridge which separates the two large, shallow scars of the adductor muscles. In front 
of the latter are sometimes seen two, linear, slightly diverging ridges, probably the 
markings of the main trunks of the vascular system. Genital markings on each 
side of the muscular scars, consisting of series of tubercles of various sizes radially 
arranged. Surface near the periphery more or less distinctly marked by numerous, 
short, irregular, radiating stria, much the strongest in the medial region. 
The variations of this species are mainly those of convexity, thickness of shell 
and alternation of striz. In the “Lower Blue beds” of Wisconsin, where this species 
is abundant, the alternation of strie is a very persistent character and the valves 
are usually flatter than specimens from other regions. 
In the Trenton shales of Minnesota S. incurvata is also a common species, often 
preserving the delicate markings of the interior. The variation in convexity here 
attains its maximum, and while the striew likewise alternate in size, this feature is 
never so conspicuous as in Wisconsin. 
This species is usually known as S. filitexta Hall. It is thought that to this form 
Shepard applied the name S. incurvata nine years prior to that given by Prof. Hall. 
One of the writers, through Mr. John M. Clarke, has endeavored to find the types at 
Amherst College, but Prof. Emerson states that no specimens of it with Shepard’s 
label attached exist at present in that collection. While the original description and 
illustrations are not very satisfactory, yet sufficient is shown, combined with the 
locality, to warrant the conclusion that the above specimens were of this widely 
distributed species. Strophomena convera Owen, proposed three years earlier than 
Hall’s name, is undoubtedly a specimen of the same species, which was derived from 
the “Blue and Grey limestone of Wisconsin and Iowa.” Probably Owen subsequently 
regarded it as identical with some other form, for in a subsequent report (1852) no 
mention is made of it. 
This species is commonly stated to occur in the Hudson River group, but a com- 
parison of specimens from that horizon with those from the Trenton will show the 
interior of the dorsal valve of the former to be entirely different in its prominent 
vascular ridges, while the space beneath the cardinal area on each side of the teeth 
in the ventral valve is filled up by a deposit of shell matter. Since Mr. U. P. James 
has applied the name Strophomena neglecta to one variation of the species identified 
by Meek in 1873 as S. filitexta, it is advisable to refer to the specimens from the 
