BEITISH FOSSILS. 



Decade XT. Plate VIIT. Fig. 14. 



OLENUSCATARACTES. 



[Genus OLENUS. Dalman, in part, (Sub-kingdom Articulata. Class Crustacea. 

 Order Trilobita. Family Olenidse.) Glabella oblong, or usually narrowed anteriorly, 

 lobed ; eye smooth, with a narrow prominent ocular ridge (Costula facialis, Angelin) 

 connecting it with the upper part of the glabella ; facial suture marginal in front, and 

 cutting the posterior margin behind ; cheeks spinous, no rostral shield; hypostome? 

 labrum oblong, narrowed at base ; pleurae 7-15, (14 typically), pointed and curved ; tail 

 with articulated axis and sides.] 



[British sub-genera. Olenus, Dalman. Body rings 11-15, head semicircular, 

 spines moderate, tail entire. — Sphcerophthalmus, Angelin (including Eurycare. id.) 

 Body rings 7-15 ; head transverse, with remote eyes and widely curved long spines.— 

 Parabolina, Salter. Body rings 12; head semi-lunar; eyes approximate ; spines 

 diverging; tail spinose. — Peltura, Angelin (not Milne-Edw.). Body rings 12; head 

 narrovt^, with approximate eyes, and no spines ; tail spinose.] 



Diagnosis. 0. ovatus \^ imcialis et ultra^ cajpite magno semilunaris 

 sipinis hrevissimis. Glabella sulcis tribus fere perfectis. Oculi antici. 

 Thoracis axis latus, pleurce vix recurvm brevispinosce, fulcro remoto. 

 Cauda, mimita, transversa, semicirculains, axi latissimo. 



Several species of the well-known Olenus of Dalman are now 

 added to tlie British list. The originally described British form is 

 Olenus micruTUS, in our Decade II., plate 9 (1849), also "Siluria,'' 

 2nd ed., p. 45, foss. 4, fig. 2. That is not, however, by any means a 

 common fossil, and it is necessary now to distinguish from it the 

 present species, which appears to be the ordinary form in the lower 

 black shales of North Wales. 



Description. — Nearly an inch and a half long, ovate, blunt at 

 both ends, the head wide, nearly one inch broad, the body much 

 narrower, tapering regularly to the tail. The head is sub-truncate, 

 the glabella moderate in size, parabolic, not so broad as the cheeks, 

 reaching forward nearly to the narrow front margin, and about the 

 width of that margin distant from it, furnished with three pairs of 

 furrows, of which the lower two are complete across. The eye is 

 nearly as far forward as the front of the glabella, and somewhat 

 [XI. viii.] 11 H 



