152 SILURIAN TRILOBITES. 



fossil to a worn Swedish specimen of A. heros, Dalman, which had lost the characteristic 

 mucro of the tail. Isotelus marginalis. Hall, formerly supposed by me to be the same, is 

 quite distinct. 



In comparing with other species, the following must be particularly noted as a very 

 close ally ; indeed, it has hitherto always been confounded with it. Both occur at the same 

 locality near Llandeilo. 



Localities. — Llandeilo Flags. Abundant in South Wales ; Llandeilo and many 

 localities in Carmarthenshire. In Pembrokeshire ; Musclewick Bay, Llampeter-Felfrey, 

 Narberth, Mydrim, and Lann Mill. In Shropshire, Meadowtown, Shelve, &c. In North 

 Wales ; Craig-y-glyn, near Llanhaiadr, in the Berwyns. But not in Scotland, Ireland, nor 

 in any Continental locahty. 



2. AsAPHUs (Basilicus) peltastes, spec. nov. PI. XXII, figs. 1 — 4. 



A. modicus, vix 4i-uncias longus, convexus, ovalis, obscure lineatus, capite cauda aquali. 

 Oculi elevati, sese spatio capitis totius longitudinis remoti. Glabella elongato-pyriformis, 

 lobis basalibus suhtrigonis isolatis. Anguli longe producti. Cauda axe 14 — \o-annulato, 

 lateribus 9 — 10-costatis. 



Certainly when I figured these specimens I did not expect to be able to determine 

 two completely distinct forms, for the general aspect is exceedingly alike in both. Yet if 

 form and proportion, difference in position of the eyes, in the form of the glabella and 

 its lobes, shape and number of ribs in the tail, &c.,be sufficient characters, we must reckon 

 for the future two distinct Llandeilo fossils hitherto confounded under one name. 



A. peltastes is probably as common as the better known A. tyr annus. It is easily 

 distinguished by the more oval, (not ovate) shape, and the equality in length of the head 

 and tail. But also notably by the small .cheeks, remote and large eyes, long and broad 

 head-spines, and the fewer ribs to the tail. The following description may serve : 



Length, judging from large fragments, not more than six inches, the breadth two and 

 a half. Strictly oval, convex ; the half-elliptic head equal in length to the tail ; the body 

 shorter than either, not exceeding the glabella in length. The glabella elongate, narrower 

 than the cheeks ; a pair of very distinct oval basal lobes (really composed of the two 

 lower pairs), isolated from the rest of the glabella, and set wide apart. A long oval fore- 

 head-lobe, which reaches quite to the concave front margin, and is more than half the 

 entire length of the head, from which it is not abruptly distinguished in front as in the 

 last species. 



The cheeks are very convex, steeply bent down towards the truly flat margin, and 

 produced behind into broad blunt spines, which are long enough to reach to the sixth 

 thorax-ring. This character at once distinguishes A. peltastes. The eyes are large and 



