38 SILURIAN TRILOBITES. 



Odontochile truncato-caudata, M'Coij. Synop*. Foss. Woody.-. Mas., t. i g, fig. 



20 (21 ?) (not Chasmops Odipi, same plate, figs. 



22, 23), 1851. 

 Phacops macrouka, Angelin. Palseont. Suecica, t. vii, figs. 3, 4, 1852.* 



P. {Chasmops) ovatus magnus, capite semilunar/', vix quam longo bis latiore, tuber- 

 culosa, caadd elongate! submucronafd mulfi-annulatd. ' Glabella pariim eonvexa, antice valde 

 dilatata, lobo frontali maximo triangulato oculum imminent i ; lobis later alibus supremis magnis 

 triangulatis quam latis multo longioribus, medianis obsoletis, basalibus contractis, cervicali 

 lato. Gence convexce nee gibba:, declivce, glabella angustiores, avgulis in cornua lata longa 

 extensis ; oculo majore, sulco circumdato, linea faciali impressd. Cauda magna trigona 

 eonvexa, apice acuto, axi lato per i longitudinis extenso, annulis 1G ; eostis later alibus 

 circa 16, fere rectis, vix interlineatis, sub apice radiantibus. 



All the above names have at various times decorated or disfigured our fossil, which 

 labours under the combined disadvantages of being very common and conspicuous, and 

 seldom at all perfect ; and also of belonging to a group of closely allied species which occur 

 in company, and have been hitherto always badly figured. I can hardly hope to have 

 remedied all these defects, and only give those synonyms of which I am assured. The 

 name Phacops conojjhthalmus, under which it is generally known in cabinets, really 

 belongs to a species with short head-spines, smaller eyes, wider cheeks, and altogether a 

 more transverse form of head, and a short tail. We must Avait for a more complete 

 knowledge of this group of trilobites ; and meanwhile our figures represent truly the most 

 conspicuous of these forms, and certainly that figured by Prof. Angelin. The numerous 

 ribs of the tail and the great head-spines readily distinguish it. 



The P. buccidenta, also figured by Angelin, has a large, many-ribbed tail, but has 

 only a small pair of lateral glabella-lobes instead of the great encroaching pair distinctive 

 of the P. macroara, and which have procured for this grotesque-looking species the name 

 among collectors of the ' Cat's-head Trilobite.' 



There are other allied species both in Scandinavia and North America ; but the group 

 appears to be peculiar to this northern zone, and does not occur in mid-Europe, as M. de 

 Barrandc has specially remarked. 



General form rather narrow, ovate, blunt but abruptly angulate in front, and shortly 

 pointed behind. The head is about as long as the tail, and not quite twice as broad 

 as long ; very convex ; semilunar, with a very wide glabella, larger than the cheeks, the 

 sides of which converge behind at about 50°. The cheeks are very convex, deeply 

 margined, and produced behind into exceedingly broad, flat, and rather lengthened parallel 

 spines, at the inner angle of which the strong marginal and still stronger neck-furrow 

 meets. 



* The cover of this excellent folio is marked 1851 ; but in order to preserve priority of date, it is 

 necessary to be exact. It seems to have appeared Jan., 1S52. 



