198 H. Woodward—Descriptions of New Paleozoic Crustacea 
elevation at the posterior angles. An inner border-line also passes 
up each side and around the front of each eye; reminding us of the 
cheek-sutures in the Trilobites. 
No sculpturing is noticeable upon the surface of the carapace ; 
but (as is the case with all the Logan-Water specimens) impres- 
sions of portions of organs are seen, the position of which is beneath 
the surface of the head. 
The basal joints of several of the palpi are visible; and, under- 
lying the Ist and 2nd thoracic segments, may be discerned the 
median appendage of the thoracic plate. 
The body is extremely slender, as compared with Péerygotus ; and 
the segments in this species (as in Sé. Powriet) had very small 
epimeral portions. The 11th and 12th segments, which are not 
preserved, were doubtless still narrower; and the telson was pro- 
bably a long styliform appendage, as in S¢. Powriet. 
Dimensions of Stylonurus Logani. —Swimming-foot : — Basal 
joint, 6 lines in length, and 5 broad ; 2nd joint, 2 lines long, 4 broad ; 
3rd, 1 inch long, 2 lines broad ; 4th, 10 lines long, 2 lines broad ; 5th 
and 6th, each 8 lines long, 2 lines broad; 7th, 6 lines long, 1 line 
broad ; 8th, 5 lines long, 1 line wide, terminating in a fine point. 
Carapace :—Greatest anterior breadth, 1 inch 3 lines ; greatest 
length, 1 inch 2 lines; width between the eyes, 5 lines ; breadth of 
inner raised margin, 1 line. Thoracic segments :—Ist segment, 2 
lines long, and 1 inch and 1 line wide; 2nd and 38rd, 3 lines long, 
and 1 inch wide; 4th, 4 lines long, and 1 inch 1 line wide; 5th, 
3 lines long, by 1 inch wide; 6th, 2 lines long, and 11 lines wide. 
Abdominal segments :—7th segment, 2 lines long, by 10 lines wide ; 
8th, 8 lines long, by 9 lines wide ; 9th, 3 lines long, by 8 lines wide ; 
10th, 3 lines long ;—here the specimen is broken, and the 11th and 
12th segments and telson are wanting. The posterior margin of 
each segment is ornamented by a row of minute spines along the 
border. 
The form of the carapace and the position of the eyes are two 
very well marked features in this genus: these, and the two 
pairs of long slender oav-like feet, sufficiently separate them from 
the rest of the family; but even the long tail-spine is peculiar. 
From the extreme rarity of its occurrence in a formation 
where other genera are so numerously represented, I am strongly 
inclined to believe this form to have been a larval condition of 
some other genus of the same group. 
I have named it Logani after my friend Sir William Logan, 
the Director of the Geological Survey of Canada. 
2. STYLONURUS ENSIFORMIS. Sp. nov. Woodcut (nat, size). 
A. tail-spine of Stylonurus, 32 inches in length (probably 
longer when perfect), 2 of an inch in width, and deeply chan- 
nelled through its entire length, from 2 at its widest part to 4 
of an inch at its extremity, was found in the Old Red Sand- 
stone, at one of the Turin Hill Quarries in Forfarshire. 
