148 BRITISH PALAZOZOIC FOSSILS. [CrusTacea. 
Ampyx Nubus (Murch. Sp.) 
Ref. and Syn.—Mem. Geol. Sury. Dee. 2. t. 10. Trinucleus nudus Murch. Sil. Syst. p. 660. t. 23. f. 5. 
Sp. Ch_—Entire animal longitudinally ovate, length about one-fourth more than the width; cephalic 
shield smooth, about two-fifths the length of the animal, about twice as wide as long; glabella very tumid, 
pyriform, with a short spine projecting from the convex front, narrowed posteriorly and with two short segmental 
furrows at each side of the base; antennary pores large, in the furrow between the cheeks and the glabella 
near the front margin; cheeks longer than wide ; thoracic segments six, pleuripedes one-third wider than the 
axal lobe; pygidiwm triangular, slightly mucronate, twice as wide as long, the axis with sixteen segmental 
furrows, the sides with nine. Average length of cephalic shield, five lines. 
At about half the length of the eye-line there is an elongate swelling which may indicate the position 
of an eye. 
Position and Locality—Very common in the shale at three miles N of Builth, Radnorshire: Well- 
field, Builth; Tre Gil, S. of Llandeilo. 
Genus. OGYGIA (Brong.) 
Gen. Char.—Body ovate, flattened, not contractile; buckler semicircular, flattened, with the angles pro- 
duced backwards into flat spines; cheeks large, continuous beneath the front margin; glabella indistinctly 
clavate, with three very indistinct lateral segmental furrows on each side; eyes semicircular, moderate, cor- 
responding in height to the two anterior lobes of the glabella, reniform ; eye-/ine coinciding with the margin 
in the front, then abruptly bending towards the eye, over which each forms the eye-lobe, and thence diverges 
to cut the posterior margin about the outer third of each side; thorax of eight segments, axis narrow; pleuri- 
pedes straight, flat, at least twice as wide as the axis, pointed and falciformly bent backwards at the 
extremities; no facets, a fine mesial pleural furrow not reaching the end; pygidiwm semielliptical, with a 
narrow distinct articulated axis, the lateral lobes also with segmental furrows not reaching the margin, and 
each having a shorter slightly oblique duplicating furrow. 
Oayera Bucui (Brong. Sp.) 
Syn. and Ref.—Asaphus id. Brongniart. Crust. Foss. and Murch. Sil. Syst. t. 25. f. 2. 
Sp. Oh.—(Female?) Broad ovate, one-fourth longer than wide; cephalic shield widely arched, about 
twice and one-fifth wider than long, as long as the thorax; plewripedes about twice and one-fifth wider than 
the axis; pygidium obtusely rounded, the width of the axis and one side lobe taken together at the anterior 
margin, slightly exceeding its length; ais of about fifteen segments, the sides with thirteen. 
(Males?) Narrow ovate, one-third longer than wide; cephalic shield semielliptical, length half the 
width, as long as the thoracic and one pygidial segments; plewripedes rather more than twice the width 
of the axis; pygidiuwm semielliptical, length slightly exceeding the width of one side and the axis, about 
twelve double segmental furrows to the sides, and fifteen to the axis. 
The figures of Brongniart, Murchison, and Burmeister, represent what 1 here suppose to be the female ; 
the more lengthened elliptical form, with longer head and more pointed pygidium, which I suspect (from 
the general analogy of recent crustacea) to be the male of the same species, does not seem to have been 
previously observed, though nearly as common in all localities as the other*; with the exception of the 
more slender contour and difference of proportion indicated above, I see no grounds for thinking there 
is more than a sexual distinction—if others should consider it a distinct species, the name O. elliptica 
might be given to it. 
Position and Locality—Very abundant in the limestone, shales, and Llandeilo flag, three miles N. of 
Builth, Pen Cerrig and Wellfield, Builth, Radnorshire ; Llandeilo, Caermarthenshire. 
* Since the above was written, Mr Salter has noticed the difference in proportion of different specimens, but without 
drawing any conclusion therefrom. (See the second Decade of the Geol. Survey.) 
