162 BRITISH PALAZOZOIC FOSSILS. [CrusTacea. 
ODONTOCHILE TRUNCATO-CAUDATA (Porth. Sp.) Pl. 1. G. fig. 20, 21. 
Ref. and Syn.—Phacops truncato-caudatus Port. Geol. Rep. t. 2. f. 1. 4. Dalmannia affinis (Salt.) Mem. 
Geol. Surv. Vol. II. Pt. 1. t. 5. f. 5. 
Sp. Ch.—Pygidium semielliptical or subtriangular, with the posterior end obtusely truncated and 
emarginate in the middle; awis gradually tapering, rather more than four-fifths the length of the pygidium, 
and about two-thirds the width of the lateral lobes in front (sometimes a little more or less), of sixteen 
or eighteen segments; /ateral lobes with a very narrow entire margin, and fifteen or sixteen broad, 
flattened ribs, each divided by a very fine impressed line. Average length of pygidium one inch three 
lines, width the same. 
The proportion of the width of the axis to that of the lateral lobes varies considerably from pressure 
both in the D. afinis and in English and Irish specimens of the P. truncato-caudatus. The figure given 
by Mr Salter of his D. affnis, in the Mem. Geol. Surv., shews the same proportion of axis to the lateral 
lobes as Portlock’s figure t. 2. f. 4. of his species. Mr Salter in the same work mentions that his species has 
fifteen or sixteen lateral ribs, which is more than the P. trwncato-caudatus, but Tyrone specimens of the 
latter now before me shew the same number; the length of the ribs is certainly the same in both. I at 
first thought D. afinis might be distinguished from the Irish species by the more acute angles at which 
the lateral ribs set off from the axis; I find this, however, to differ on two sides of the same specimen, 
and is as marked occasionally in one species as in the other. It is only the pygidium that has occurred 
to collectors as yet in England, and in the absence of distinctive characters I have reunited the species. 
Position and Locality —Shales of Blain y Cwm, W. of Nantyre, Glyn Ceiriog; the Hollies, Church 
Stretton, Shropshire. 
Explanation of Figures.—P\. 1. G. fig. 20. Pygidium natural size (type specimen of the Phacops affinis, 
Salt.) Fig. 21. Small specimen. 
Subgenus. Porriockia (M*Coy). 
Gen. Char.—Cephalic shield truncato-orbicular, lateral angles not produced into spines; glabella very 
large, broad in front, sides converging to a narrow base behind and having (on the outer crust) but one 
small, segmental furrow at base; cheeks small, triangular; eyes large, reniform; eye-lines extending from 
the base of the eye to the outer margin, a little in front of the angles; abdomen of eleven segments, 
resembling those of Phacops; pygidiwm small, semielliptically rounded, with a simple, entire margin, of 
about five to eight segments to the axis and about five to the lateral lobes, each with a very fine mesial 
divisional line in the distal portion. 
I originally proposed this genus in my Sil. Fos. of Ireland in 1846, for those species of Phacops in which 
the two anterior pairs of great segmental lobes of the sides of the glabella were deficient, and the lateral 
angles of the cephalic shield were not prolonged. The Calymene Bufo of Green, C. macrophthalna of 
Murchison, &c. being the types of the genus, which has been recognised as a natural group by Gold- 
fuss, Burmeister, &c., as well as by my friend Col. Portlock, to whom I dedicated the group. 
PortLockta? APICULATA (Salt. Sp.) Pl. 1. G. fig. 17 to 19. 
Syn.—Phacops apiculatus (Salt. in Ap.) 
Sp. Ch.—Cephalic shield moderately convex, semioval, length slightly exceeding half the width: glabella 
semicylindrical, front obtusely rounded, not very much wider than the base, sides nearly straight, converging 
from the front to the wide neck-furrow; segmental furrows three, nearly equidistant, on each side, the 
two upper (or anterior) pairs very fine and almost obsolete, basal pair very strong and gently arched 
backwards ; eyes long, narrow, semilunar; cheeks triangular, longer than wide, sloping from the eye to the 
rounded lateral angles, furrow at the posterior margin much stronger than the one at the external margin ; 
surface smooth; pygidium (supposed of the same species) depressed, semielliptical, length about two-thirds 
the width, slightly pointed, margin narrow, entire, axis narrow, tapering, strongly projecting at the end, 
