Geology of the St. Croix Dalles. — Berkey 291 
and curving a little upward at the sides; occipital ring wider in the 
middle curving forward towards the extremities." 
"Facial suture directed slightly inwards from the anterior margin, 
and thence curving gently outwards, it follows the line of the palpe- 
bral lobe nearly to the occipital furrow, when it turns abruptly out- 
wards. Dorsal furrows rather wide and deep, continuing rather less 
distinctly round the front." 
"Fixed cheeks narrow, expanding in the direction of the eye, and 
separated from the palpebral lobe by a long distinct sigmoid groove: 
posterior limb narrow, its extent unknown. Frontal limb of mod- 
erate width, separated from the glabella by a narrow groove, marked 
along the middle by a broad shallow transverse furrow, which is 
stronger at the sides and sometimes nearly obsolete in the middle; 
anterior margin flattened, and a little produced in the middle." 
Differences are chiefly in points relating to the frontal limb. The 
smaller specimens dififer only in having a narrower frontal limb than 
those which are of twice the size. While those few specimens which 
are very large have the frontal limb anterior to the groove very much 
produced into a broad and promment shovel-like projection, whicn 
adds much to the differences in comparative length of head in dif- 
ferent specimens. The specimens vary in size from a length of 5 
mm. to a length of 25 mm. for the head of the largest one found. 
On account of this seemingly constant variation with the size 
of the specimens, it has been considered most probable, in the ab- 
sence of other marked differences that all belong to the same species 
and that differences in size with accompanying development noted 
above indicate the comparative maturity of different individuals. 
Formation and locality: Franconia sandstone, Franconia, Minn. 
Ch. AFTER III. Summary and Correlation. 
The vertical range of some of these species is shown to 
be much greater than before supposed. 
Lingiilepis pinniformis Owen, is most abundant near the 
l)ase of the formation in the calcareous layers of the shales, 
but specimens are also found in the Taylor's Falls conglom- 
erate indicating a vertical range of more than 125 feet. Above 
the Dresbach no specimens of this species have been identi- 
fied in this area. 
Tryblidiinn barabnensis (Whitfield), is identified from 
rhe Jordan sandstone while the related forms T. eonvexi(»i, 
n. sp., and 7". extensnni, n. sp., are from the marginal con- 
glomerates of the Dresbach. Therefore the range exhibited 
by these similar species is about 200 feet. 
