BRITISH FOSSILS. 



Decade II. Plate X. 

 AMPYX NUDUS. 



[Genus AMPYX. Dalman. (Sub-kingdom Articulata. Class Crustacea. Order 

 Entomostraca. Family TrilobitEe.) Glabella tumid, armed with a frontal spine ; head 

 with simple, unexpanded margins ; angles spinous ; no facial suture ; no eyes ; body rings 

 5 or 6 ; tail entire-margined, margin deflected ; hypostome ?] 



Diagnosis. A.latus; capite semicirculari, spina frontalibrevi; angulis 

 longespinosis ; glabella vix producfa, laterihus bilobatis ; thorace articiilis 6 ; 

 Cauda lateribus 8 — 9 sulcatis. 



Synonyms. Trinucleus nudus, Murchison (1839), '^Sil. Syst.," p. 660, 

 pi. 23, f. 5. 



Description. — General outline broadly oval ; body much depressed ; 

 the general axis, consisting of glabella, axis of thorax, and axis of tail, 

 forming a lanceolate, convex, central elevation, narrowing posteriorly. 

 Head, thorax, and tail of equal length. The first is rounded, with 

 the outline, in front, slightly prominent, and the whole less than a 

 semicircle ; the last is slightly triangular. Glabella somewhat claviform, 

 rounded and convex in front, narrowing behind the middle, and slightly 

 widening out at its junction with the neck furrow ; it is marked at each 

 side by two or three indistinct furrows, and, towards its centre, by two 

 very oblique furrows, which form small elliptical elevated spaces, one 

 on each side, bounded by rounded and curved folds, below the level of 

 the rest of the glabella, and appearing as if distinct from it. From the 

 front of the glabella projects a slender subulate spine, which, in all 

 examples hitherto met with, is rather less than the length of the head : 

 it is not continued as a keel on the central surface of the glabella. 

 The neck furrow is well marked,, and the neck fold elevated. The 

 cheeks are broad, depressed obliquely in their centres ; the depres- 

 sion proceeds from near the upper extremity of the glabella lobes, 

 and continues obliquely outv^ards, with an obscure curve towards, but 

 not touching the margin. Between the depression and the hinder por- 

 tion of the glabella the cheek is gently tumid, and likewise between the 

 depression and the outer margin. The neck furrow runs straight and 



[ll. X.] 2 K 



