Crustacea. | LOWER PALAXOZOIC ARTICULATA. 153 
gular, gibbous, the angles prolonged backwards into sharp spines; eyes large, prominent, near the outer 
margin ; eye-line coming from the front to the eye with an outward curve, and extending thence with an out- 
ward curve to a little in front of the angle; thorax with nine segments ; plewre broad, flat, straight, and 
longitudinally furrowed, one half only reaching the margin, the other thicker and produced beyond into a 
slender spine, bent abruptly backwards ; pygidium small, quadrate, axis of four segments, the first three narrow, 
the last large, semicircular; side lobes flat, with three small segmental furrows, and the margin produced 
backwards into six slender spines. 
The genus Trochurus of Beyrich was originally founded on the head of this genus and a tail belonging 
to the group of Lichas, and he only figured the latter part; subsequently Barrande proposed the generic 
term Staurocephalus for the head alone, which was adopted by Beyrich in his subsequent memoir, “ Unter- 
suchungen iiber Trilobiten,” for the head; and the tail, formerly called by him Trochwrus, for which he had 
now found the true head, was placed in the genus Arges; lastly, Hawle and Corda figured and described 
the entire animal, and restored to it Beyrich’s old name Trochurus; and to the originally figured tail of 
Trochurus and its subsequently found true head they gave the name Corydocephalus. As this would be 
productive of much confusion, I have used Barrande’s name (sanctioned by Beyrich) for the animal to 
which the head described belongs, and to the tail originally figured by Beyrich as the 7. speciosus, the 
type of this genus 7vochurus, (subsequently named by him, with its appropriate head, Arges speciosus, and 
perfect specimens of which have been figured by Hawle and Corda in their “ Monog. bohm. Tril.” under 
the new name Corydocephalus flabellatus) I have retained the original name Trochurus. 
STAUROCEPHALUS Murcuisoni (Bar.) PI. 1. F. fig. 15. 
feef —Barrande, Notice, p. 53. 
Sp. Ch.—Anterior half of glabella an oblate spheroid, slightly wider than long, posterior half abruptly 
narrowed to a small stem-like, cylindrical neck, about one-third the diameter of the front half; cheeks 
hemispherical ; surface with a strong granulation, the granules sharp, subequal, and nearly their diameter 
apart. Length two and half lines, width four lines. 
I have only seen the head of this interesting addition to our list of British Trilobites, which I detected 
in a small parcel of duplicate Trinuclei labelled Trinucleus seticornis by Mr Salter, to whom they had 
been lent to illustrate (I believe) his paper on 7rinucleus ; but the resemblance to that species and genus 
seem to me deceptive, the large eyes alone separating the heads easily, in my opinion. 
Position and Locality.—Very rare in the limestone of Rhiwlas, W. of Bala Lake, Merionethshire. 
Explanation of Figures—P\.1. F. fig. 15. Glabella and part of cheeks, natural size.—Fig.15 a. Ditto 
magnified. 
Genus. CERAURUS (Green.) (as here redefined.) 
= Chirurus (Beyrich). 
Gen. Char.—Cephalic shield granulated, semicircular, lateral angles prolonged into spines; glabella 
clavate, reaching the front margin, gibbous, with three subequal segmental furrows on each side, the basal 
one retroflexed; eyes small in the midst of the cheeks; eye-line going from their base directly to the 
outer margin, which they cut considerably in front of the angles; thoraw of eleven segments; pleura wider 
than the axis, each having its origin thickened into a large oblong tubercle cleft by a deep diagonal 
pleural sulcus; a little beyond this a small rounded tubercle, beyond which the extremity is flat and 
faleately pointed; pygidiwm with a short four-jointed axis, and the margin produced into three strong 
spines on each side, the anterior largest. 
A careful examination of the details of the original specimen of Green’s Cerawrus, recently published 
by Hall in his Paleontology of New York, satisfies me there is no difference between that genus and the 
Chirurus of Beyrich, as restricted by Hawle and Corda; which latter I therefore propose to suppress as 
a synonym, Green’s type being specifically distinguished by the unusual length of the anterior marginal 
spine of the pygidium on each side. 
x 
