90 SYSTEMATIC AREANGE^iIENT 



This species approximates very nearly to the preceding, but can be readily distinguished 

 from it. The glabella, which in other respects is similar, is not quite so broad at the 

 anterior part as in Ph. lafifrons, and its sides are rather angular, or at least bent in this, but 

 extend in quite a straight line in the former ; the eyes, which are small, are situated beside 

 the anterior part of the angle, close to the margin of the head, and have only few lenses 

 (from two to three rows) ; the circumference of the cephalic shield is more broadly reflexed, 

 and does not present quite so acute an edge ; the posterior margin seems to be less produced 

 The body and caudal shield are not yet known ; the individual which I examined was 

 without a shell, and therefore quite smooth. 



Group B. Species with a glabella divided into lobes ; the isolated little tubercles on 

 the posterior angles are wanting, and instead of them there is a transverse protuberance. 



Remark. — The glabella in this group has always three lateral lobes between the large trapezoidal 

 front lobes and the posterior margin of articulation, therefore four lobes in all (including the anterior 

 and chief protuberance). Of these the third is sometimes very small, and on that account appears 

 occasionally to have been overlooked. 



Sub-Groiijj {a). The posterior extremity of the caudal shield rounded or obtuse.* 



3. Ph. anchiops : Tuberculo capitis elevato, lobis lateralibus obsoletis (s. mutilatis); oculis maximis; 

 rhachi caudse 12 anuulata, costis decern. Long. 2-4". 



Bef. — Calt/m. ff«r/<. Green, J/o». o/ yn7o(5. 3.5, Mod. 7. Emmr. Z)m«-^. 22. 8. Milne 

 Edw. Or. iii, ,325, 15. Var. minor. Asajjh. Wetlimlli, Green, Mod. 20. 



Locality. — In a black limestone of North America, at Ulster and Murron (New York). 



The plaster cast which I examined, and which is in the Berlin Museum, reminds one 

 of the preceding species, and the present is principally distinguished by a longer urn-shaped 

 glabella, sulcated posteriorly, in which, however, I could not perceive any distinct lateral 

 lobes, with an acute outline as usual. On the other hand, there is only an im])erfect lobe, 

 which is isolated, and projects near the tubercle of the eye at the glabella ; and instead of 

 the peduncle, I notice before the margin of articulation a short transverse prominence 

 scarcely disconnected. The original from which the cast had been taken was, however, 

 evidently impei-fect. The body has distinctly eleven joints ; there are twelve joints of the 

 caudal shield, and ten lateral ribs towards the posterior part, but rather indistinct. Green, 

 owing to this, enumerates only twenty rings in all, which would leave nine for the tail. 



Remark. — Asaph. Wetherilli, of which I examined a plaster cast at Berlin, appeared to me to be 

 a smaller individual of the species described by Green as Cal. anchiops. The head is, however, so in- 

 distinct, that accurate determination is impossible ; I was able to recognize the eleven body joints with 

 certaintv. 



* From observations which I have made on Phacops sclerops and P. procerus, and which I shall 

 subsequently make known more in detail, I believe myself justified in inferring that elongated pointed 

 angles at the cephalic shield existed in most of the species of Phacops liaAnng a lobed glabella, but were 

 broken off with the calcareous shell. These species therefore can no longer be grouped according to 

 the form of the cephalic shield. 



