CRUSTACEA. 83 



constricted at its base as in Conolichas. The third pair of lateral lobes which 

 is usually present in typical species of lloplolichas. is almost if not quite obso- 

 lete in L. hylo&m, and the species hears the same relation to the Silurian forms 

 of lloplolichas as L. Eriopis does to the Silurian species of Conolichas (See 

 observations under the description of L. Eriopis.) 



Distribution. Upper Helderberg group. In the limestone, Province of Ontario. 



[s.-g.] ARGES, Goldfuss. 1839. 

 Lichas (Arges) contusus, n. sp. 



PLATE XIX B, FIGS. 3-6. 



Cephalon broadly semi-oval in outline. Surface sub-equally trilobate, evenly 

 convex. 



Glabella with an elongate frontal lobe, having a width equal to that of each 

 of the lateral lobes, and bounded by furrows which are parallel for three- 

 fourths their length, diverging near the frontal margin, thus greatly increas- 

 ing the width of the lobe upon the anterior border. First and second pair of 

 lateral lobes coalesced into a single pair of relatively short, obliquely pyri- 

 form lobes, terminating posteriorly sooner than the frontal lobe. The third 

 pair of lateral lobes are obsolete or represented only by tubercles in the 

 occipital furrow. 



The fixed portion of the cheeks is convex behind the eye-nodes, and abruptly 

 deflected to the occipital furrow. Occipital furrow broad and deep upon 

 the axial line at the posterior termination of the frontal lobe, narrowing 

 upon the cheeks and bending forward to very near the ocular node ; occipital 

 ring axially convex, relatively narrow, making a marked anterior curve upon 

 the sides as it turns toward the presumably very narrow and slender free 

 cheeks. Frontal border narrow and thickened, with a strong marginal 

 sulcus. Surface covered with closely set and evenly distributed tubercles. 

 The remaining parts of the animal are unknown. 



Dimensions. Two specimens of the intra-sutural portions of the cephalon 

 have a length of 7 mm., and a width of 11 mm. 



