Silurian.} PALJiONTOLOGY OF VICTORIA. \_Trilobitcs. 



Plate XXII., Figs. 1-7, and Plate XXIIL, Figs. 7-10. 

 PHACOPS (ODONTOCHILE) CAUDATUS (Brong.). 



[Genus PHACOPS (Eiimerich extended). (Sub-kingd. Articulata. Class Crustacea. 

 Order Entomostrac.-i. Fam. Trilobitidie.) 



Gen. Char. — Head large, with the angles prolonged backwards into large spines ; glabella 

 clavate, wider in fr.iut than at the base, and marked with three strong segmental furrows j eyes 

 Tery large, reuiform, with a coarsely granular, largely facetted cornea ; thoracic segments 

 11 ; facial sutures cutting the lateral margin of the head in front of the angles. 



Sub-genus. — Otluntoc/iile CHawle and Corda) = X)o/man»/a (Emmerich) (not of Robineau- 

 Desvoidy).* General form, buckler, glabella, eyes and et/e-lines, as in Phacops, but the lateral 

 lobes of the glabella more equal ; not contractile ; thorax of 11 segments ; pleuripedes curved 

 backwards and generally pointed at their extremities ; facets very long, narrow rhomboidal, 

 slightly defined ; pleural groove strong, slightly sigmoid and oblique (not angulatcd) ; pygidium 

 elongate, generally pointed ; axis with from 12 to 22 segmental furrows, sides with fewer (about 

 half the number) strong ribs, usually duplex, confluent at their ends with the thickened entire 

 margin ; hypostoma with a dentate edge. 



Sub-genus. — Porllockia (JlcCoy f) — Cephalic shield truncato-orbicular, lateral angles not 

 produced into spines ; glabella very large, broad in front, sides converging to a narrow base 

 behind and having (on the outer crust) but one small segmental furrow at base; cheeks small, 

 triangular ; eyes large, reniforra ; eye-lines extending from the base of the eye to the outer 

 margin, a little in front of the angles ; abdomen of 11 segments, resembling those of Phacops; 

 pygidium small, semi-elliptically rounded, with a simple entire margin ; about 5 to 8 segments 

 to the axis, and about 5 to the lateral lobes, each with a very fine mesial divisional line in the 

 distal portion.] 



Description. — General form ovate j varying' from 2 to 4 inclies long-. Head 

 depressed, semi-ovate, with a more or less angulated projection of the margin in 

 front, about twice as wide as long, excluding the acutely angular tapering flattened 

 posterior lateral angles which extend backwards and a little outwards as far as the 

 7th segment of the thorax, confluent at base with the thick outer and posterior 

 margin, the bounding sulci of which do not quite meet. Glahella coarsely and 

 irregularly granulated, broadly clavate, rounded in front, moderately convex, sides 

 nearly straight, converging to the narrowed neck ; neck furrow and two succeeding 

 segmental furrows strong-, nearly equal, transverse, the anterior segmental furrow on 

 each side so oblique that the inner ends are only as far from the 2nd as that is from 

 the basal one, while the outer end is in front of the 2nd by a space equalling the 

 neck furrow and 2 succeeding furrows. Eye large, extending from upper end of 



* This genus was first noticed by Emmerich under the name Dalmannia, which was used 

 fifteen years before for a genus of insects by Robineau-Desvoidy. I therefore use the name of 

 Hawle and Corda, who do not allude to Emmerich's having previously ch.aracterised the genus. 



t I originally proposed this genus in my Sil. Fos. of Ireland in 1846 for those species of 

 Phacops in which the two anterior pairs of great segmental lobes of the sides of the glabella 

 were obsolete, and the lateral angles of the cephalic shield were not prolonged ; the Calymene 

 Bufo of Green, C. macrophthalma of Murchison, &c., being the types of the genus. 



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