60 SILURIAN TRILOBITES. 



rower and more pointed, and the lobes less crowded. It need not be compared with 

 P. stellifer, Burm., as that species has eleven broadish spines. 



We must wait a little for more perfect information. 1 It is certain that a very beautiful 

 Trilobite is yet to be found in Cornwall and South Devon, and collectors should look care- 

 fully for it. 



Locality. — Middle and Lower Devonian. Torquay, South Devon ; Slates of Lis- 

 keard, Cornwall (Coll. Mr. Pengelly and Mus. P. Geology). 



Family— CHEIRURIDiE. 



A group whose limits are not yet fully defined, if, as I suppose, it should include all 

 the forms cited below. The Cheiruridae proper have really more of the characters of 

 the Phacopidae than appears at first sight, for these loosely built Trilobites have the eyes 

 reticulate externally, though on a smaller scale than PJuicojjs, and the facial suture ends 

 upon the exterior, not the posterior, margin. The normal number of body-rings is eleven. 

 With these points of resemblance, important as they are, the analogy ceases, for the 

 short, oblique furrow and free ends of the nodular pleurae give a very marked aspect ; 

 and the tail is of few joints, and the ends of their pleurae are also free. 



The genera thus included are Cheirurus proper and its subgenera, and S/jharcxochus, 

 with Ampldon and Placoparia? Staurocephalus and Deiphon must follow these. 



But the other group, Encrinurus, Cybele, Cromus, Zethis, &c, though they agree in 

 the marked position of the facial suture, have so many differences of habit that I am 

 doubtful if they should not form a distinct family. The long prominent eyes may or may 

 not be granulated ; we have no evidence of it. But there is a strong resemblance to the 

 family of the Acidaspidae, which follows next, and I shall reserve the description of both 

 of these groups till all the available material is collected. 



CHEIRURUS, Beyrich, 1845. 



Head strongly trilobed ; glabella with three lateral lobes, the basal ones circumscribed ; 

 eyes facetted minutely ; facial suture ending on the external margin [under side of head 

 with a transverse rostral shield, Barrande]. Cheeks generally scrobiculate. Labrum 

 inflated, oblong, truncate, with a pair of furrows and small lateral auricles. 8 Thorax of 

 ten, eleven, or twelve joints, variously sculptured in the different subgenera. 



1 Goldfuss's introductory remark to his ' Essay on Trilobites' is still very applicable to the group, it 

 not quite germane to the subject. I beg to refer the curious reader to it (' Neues Jahrb.,' 1843, 

 p. 537). 



2 There is also a blind Devonian genus of this group, from Africa, in Lower Devonian, — Typhloniscus. 

 See Plate VI, figs. 12, 13. We want a term, and I propose the above for these lateral portions of the 



labrum, very distinct in Cheirurus, Lickas> &c. ' 



