CRUSTACEA. TRILOBITA 



305 



Fig. 131. Olenus cataractes, from 

 the Lingula Flags. Natural 

 size. 



2 to 8 segments. Lower Cambrian to Tremadoc Beds. Ex. C. 

 li/elli, C. sulzeri, Lower Cambrian. 



Olenus (fig. 131). Body oval ; head-shield larger than the 

 pygidium, with a narrow border, 

 and with genal spines ; glabella 

 not reaching the anterior border, 

 and not expanding in front, 

 usually with three pairs of fur- 

 rows ; facial sutures extend from 

 the posterior margin (near the 

 genal angle) to the front border ; 

 eyes a little in front of the 

 middle of the cheeks, and united 

 to the front of the glabella by 

 an eye-line. Thorax of from 12 to 15 (typically 14) segments ; axis 

 narrow, pleurae with short points. Pygidium small, with 3 or 4 

 segments indicated on the axis, and with entire border. Lingula 

 Flags to Tremadoc Beds. Ex. 0. gibbosus, 0. cataractes, Lingula 

 Flags. Parabolina, Peltura, Parabolinella, Leptoplastus, Eurycare, 

 and Sph&rophthalmus are related to Olenus and usually regarded as 

 sub-genera of it. 



Angelina. Body oval. Head-shield with long genal spines, 

 glabella parabolic, without furrows; eyes small, near the middle 

 of the cheeks. Thorax with 14 or 15 segments, pleura? facetted. 

 Pygidium short, margin provided with two teeth, axis of 4 or 5 

 segments. Tremadoc Beds. Ex. A. sedgivicki. 



Calymene (fig. 123). Head-shield semicircular, genal angles 

 rounded, occasionally pointed ; glabella inflated, broadest behind, 

 with three pairs of lateral furrows separating three globular lobes on 

 each side. Eyes small, prominent. Facial sutures extending from 

 the genal angles to the anterior border, where they are connected 

 by a transverse suture below the margin. Thorax of 13 segments, 

 axis prominent, pleurae grooved and facetted. Pygidium with 6 to 

 11 segments, margin entire. Arenig to Upper Ludlow. Ex. C. 

 tuberculata, Wenlock Limestone. 



HomalonotllS. Body large, elongated, with indistinct triloba- 

 tion. Head-shield broad, genal angles rounded, furrows on the gla- 

 bella indistinct or absent. Eyes small. Facial suture passing from 



w. p. 20 



