164 BRITISH PALHOZOIC FOSSILS. [Crusracea. 
presence, coarse reticulation, and large lenses, gives an appropriate name to the genus, and one which 
is in antagonism with that I have adopted for the present group*. Chasmops differs, besides, from both 
these genera in the almost complete suppression of the middle pair of segmental lobes of the glabella. 
Cuasmors Opint? (Kich. Sp.) Pl. 1. G. fig. 22, 23. 
Ref. and Syn.—Calymene Odini Fich. Sil. Syst. in Esthl. Phacops felinus Salt. in Ray ed. of 
Burmeister, p. 125. Asaphus Powisii (head only) Murch. Sil. Syst. t. 23. f. 9. 
Sp. Oh.—Cephalie shield semicirculcr, lateral angles extending backwards into triangular flat spines ; 
glabella gently convex, nearly one-fourth wider than long, broadly clavate, first segmental furrow of each 
side arched obliquely backwards and inwards, having about one-fourth the width of the glabella between 
them, second pair of furrows inclining forwards and inwards so as nearly to meet the ends of the first 
pair; space behind the anterior segmental furrow very large, triangular, extending nearly to the neck- 
furrow, middle lobe entirely obsolete or reduced to a minute granule; third lobe much larger but less 
than the neck-furrow; neck-segment thick, strongly defined; cheeks triangular, slightly convex, a little wider 
than high; eyes rounded, their diameter less than half the length of the first lateral lobe of the glabella, 
close to the axal furrows; swrface granulated; pygidium elevated, marginal third deflected almost vertically, 
axis of ten segments, convex, two-thirds the width of the side-lobes in front, abruptly narrowed after the 
fifth segment, lateral segments thick, about eight, each divided by a fine mesial line; entire part of 
margin narrow. Average length of head nine lines, width one inch nine lines; length of pygidium nine 
lines, width one inch four lines. 
On examining the specimen figured on the plate by Mr Salter, I find that the angles are broken, but 
shew evident traces of the large spines on both sides, and another specimen from Applethwaite Common 
shews one of them distinctly, and of great size. 
Position and Locality—Common in the limestone at Llandeilo, Caermarthenshire; in the beds under 
the limestone Glyn Ceiriog, Denbighshire ; Llansantfraid; Alt yr Anker, Meifod, Montgomeryshire ; 
Applethwaite Common, W estmoreland; Coniston Water-Head, Lancashire; Tre Gil, S. of Llandeilo; 
Selottyn Road. 
Explanation of Figures.—P). 1. G. fig. 22. Cephalic shield, natural size (Mr Salter’s figure on this plate 
erroneously represents the angles as rounded—they are produced into long, flattened spines, partially broken 
off in the specimens) ; schists of Llansantfraid.—Fig. 23. Pygidium, natural size, same locality. 
Genus. CALYMENE (in a wider sense than heretofore). 
Gen. Char—Lateral angles of the head obtusely rounded, exactly bisected by the facial sutures ; 
eyes small, ‘“hiant ;” glabella narrower in front than at the base; thoracic segments thirteen. 
These trilobites differ remarkably from Phacops in the structure of their small eyes, which are seldom or 
never preserved, seeming to have been of so delicate a nature as to fall out on the animals death, leaving a 
hole in the cephalic shield where they were set, whence Dalman’s term “hiant.”. The head differs from 
Phacops in its blunt lateral angles, and the glabella being wider at base than in front, and in the course 
of the eye-line; the body differs in having thirteen instead of eleven segments. 
The two following are British subgenera ; 1, Calymene, 2, Homalonotus. 
Subgenus. CALYMENE (Brong.) 
Gen. Char.— Buckler semicircular, with a reflected anterior margin and obtusely rounded lateral angles ; 
glabella narrower in front than at base, sides marked with three maxillary furrows and tubercles on each 
side, the anterior smallest; eyes about the middle of the cheeks, reniform, prominent, strongly facetted ; 
eye-line advancing to the anterior margin, where being confluent with the marginal suture it joins that of 
the opposite side; over the eye it makes a small curve outward, defining a semicircular eyelobe, from whence 
* [ need scarcely say, that of course, both this genus and Calymene had originally eyes, like other Trilobites in 
general structure, but differing remarkably from their allies in form, or strength of cornea, 
