74 
GEOLOGY OF THE FOURTH DISTRICT. 
Fig. 8 a, is apparently a young individual of the same species. It so frequently occurs of 
this oblique form, that I have presented a figure. 
This shell is abundant in the upper and lower green shale at Wolcott, Sodus and other 
places in Wayne county, and less common at Rochester and the localities at the west. A 
similar form, however, is abundant in the upper part of the limestone of this group at Lock- 
port, the variation perhaps due to the nature of the matrix. This, or another variety is 
abundant in rocks of this group in the Third District, and considered among its disinctive 
fossils. 
9. Calymene 1 trisulcata. — This little Trilobite is one of the fossils occurring in the 
green shale at Rochester, associated with those here described. Body with eleven articula¬ 
tions ; tail with four distinct articulations on each lateral lobe, and six on the central one ; the 
central lobe of the head is marked on each side by three indentations or furrows, which ex¬ 
tend about one-third across it. In these furrows it somewhat resembles the Triarthrus, 
and more nearly the Calymene1 Downingice of the Wenlock limestone.* The structure and 
arrangment of the eyes, however, differ from the latter; and according to the strict definition 
of the genus Calymene, it should be separated. Our specimen is much smaller than C. 
Downingice, its length being but half an inch. 
10. Agnostus latus. — Natural size, and magnified. This fossil is placed among crustaceans 
by naturalists. It usually presents two views : one with a narrow depression in the centre 
and an elevation on each side, and flanked by an expanded border ; another form where there 
is only a slight broader depression in the centre, and no elevated ridges — probably the two 
sides of the creature. This fossil occurs in great numbers in the upper green shale at 
Rochester, and also at other localities. In the Third District it occurs in millions, and though 
so small, yet constitutes a large proportion of some thin sandy and shaly layers in rocks of 
this group south of Utica. 
This is the lowest position in which this fossil is known in New-York. It was discovered 
in the green shale at Rochester, in the second year of the survey; and since that time, it 
has been found in many other localities. 
11. Tentaculites minutus. — This fossil occurs with the Agnostus and other forms in the 
green shale at Rochester. The figures are of the natural size, and magnified. It is dis¬ 
tinctly annulated near the base, but apparently smooth above. Its minuteness, and the 
compressed and flattened form in the shale, renders a full examination of the specimen dif¬ 
ficult. 
12. Graptolites Clintonensis. — This fossil occurs in great abundance in the upper green 
shale at Sodus, Williamson, Rochester, and numerous intermediate points. The serrae or 
teeth are usually long, and bent or recurved, though others associated with them differ in this 
respect. I have not yet decided whether one or two species exist. At Sodus the shaly 
laminae are completely covered with these bodies, broken into short fragments, and lying in 
great confusion; more perfect specimens are often found with Strophomena cornuta. In the 
Silurian System, p. 655, pi. 14, fig. 3. 
