182 BRITISH PALAZOZOIC FOSSILS. [CrusTacgea. 
the middle extending the entire length, and one on each side not reaching the front margin; within, and 
anterior to the ends of these latter, are two small, obliquely longitudinal sigmoid ridges, extending inwards 
and forwards towards the mesial ridge ; posterior part of body naked, tail terminating in three large, strong, 
equal triangular spines, the middle one bayonet-shaped, with a triangular section, the lateral ones flattened. 
I have not as yet detected any trace of eyes in this genus, which seems closely allied to Apus. 
I have examined four species from the carboniferous rocks of Ireland, but the only British example I 
have seen is a specimen in the collection from the black carboniferous limestone of Derbyshire, indistinctly 
preserved, but most probably the tripartite tail of a new species, allied to D. Colei (Port.) “ Geol. Rep.” t. 12, 
and to the D. Scouleri (M°Coy), figured in my “Synopsis of the Carb. Foss. of Ireland,” t. 23. f. 2, from 
the black shales of Aughnaclough, Clogher. In this species the central, angularly-ridged spine is about ten 
lines long; the two lateral spines about one inch five lines long, coarsely suleated longitudinally by only three 
or four strong ridges :—this great excess of the length of the lateral over the medial spine seems to characterise 
the species very well, and I would provisionally call it Dithyrocaris lateralis (M°Coy) ; when imperfect, the 
coarseness of the few large sulci of the lateral spines easily distinguishes those parts from the two figured 
species alluded to. 
Family. TRILOBITAD. See page 138. 
Subfamily. ASAPHINA. See page 159. 
2nd Subgenus. GRIFFITHIDES (Porth) 
Gen. Char.—Elongate, oval, buckler semielliptical with produced lateral angles; glabella without seg- 
mental furrows, gibbous, pyriform, contracted to a narrow neck posteriorly, from whence a small gibbosity 
extends on each side obliquely upwards and outwards, forming a nucleus to the eyes, which are small reni- 
form, covered by a thick smooth cornea; thoraw of nine segments with distinct facets; pygidium semioval, 
both the axis and lateral lobes with distinct segmental furrows (duplicate in the latter) and entire margin. 
Distinguished from the Silurian genus Asaphus by having one more segment to the thorax, and distinct, 
duplex, segmental furrows to the lateral lobes of the tail. 
The strongly contracted base of the pyriform glabella, absence of glabellar segmental furrows, and the 
thickness of the outer cornea of the eye obscuring the reticulation, separate this genus from the other car- 
boniferous group Phillipsia. 
GRIFFITHIDES, MESO-TUBERCULATUS (M‘Coy). Pl. 3. D. figs. 10, 11. 
Ref—M Coy, Ann. Nat. Hist. 2nd Series, Vol. IV. 
Sp. Ch.—Cephalathorax ten lines wide; glabella widely pyriform, broadly rounded in front, gently 
convex and narrowing posteriorly with concave sides, very minutely granular ; length five lines, width four 
lines; cheeks triangular, flat, smooth; eyes large, reniform, very minutely reticulated, with a large convex 
eye-lid, connected with the base of glabella by a small, oblique, oval nucleus ; limb broad, convex, with nine 
or ten imbricating strize, two-thirds concealed in front of the glabella, ending posteriorly in acute spines as 
long as the glabella; neck-segment broad; pygidiwm six lines long, and seven and a half lines wide; axal 
lobe two lines wide, cylindrical, slightly tapering, of sixteen rings, each ornamented with about ten lengthened 
oval tubercles; lateral lobes depressed, of ten broad, flat divisions, each having a fine impressed line running 
close to its posterior margin; smooth to the naked eye, but with a strong glass, one or two rows of minute 
crowded granules are seen; margin wide. 
The axal lobe of the pygidium being strongly tuberculated and the lateral lobes nearly smooth, separate 
it from all other carboniferous trilobites I know of. It is allied to the G. calcaratus (M*Coy), and G. longi- 
spinus ( Port.) 
