134 Transactions of the Royal Canadian Institute 



this second dorsal carapace spine and the posterior rostral spine is the 

 first carapace spine, which is hooklike and more slender than the second. 



Directly ventral to the first carapace spine is the base of the supra- 

 orbital spine. Seen laterally this spine appears wide at the posterior end 

 where it is one-half the depth of the rostrum at the orbit. It is cut ofif 

 anteriorly in such a way as to end in a sharp spine but the dorsal edge 

 is straight. Seen from above the supraorbital spine is needle shaped, 

 just reaching to the posterior part of the base of the posterior carapace 

 spine. 



Suborbital spine strong, pointed, base just ventral to anterior end 

 of supraorbital spine, and its anterior end ventral to the anterior end 

 of the third dorsal rostral spine. At the ventro-anterior angle of the 

 carapace is a sharp stout pterygostomial spine which points slightly 

 downward. It is directly ventral to the suborbital and at a distance from 

 it equal to that between the suborbital and the dorsal side of the rostrum. 

 Pterygostomial spine smaller than suborbital. Carapace convex between 

 them. 



Passing posteriorly from the pterygostomial spine the depth of the 

 carapace increases till at the level of the second dorsal carapace spine it 

 is 0.6 of the length of the carapace. Posteriorly the ventral border rises 

 slowly while the dorsal edge falls. In the posterior one-fifth of the cara- 

 pace the dorsal surface rises, then suddenly falls producing a rounded 

 flange at the dorso-posterior end of the carapace. Posterior to this the 

 dorsal and ventral edges meet in a rounded portion of the carapace 

 which is overlapped by the first abdominal segment. 



The first abdominal segment has the ventral edge well rounded, and 

 is wider at the dorsal than at the ventral border, and is overlapped ven- 

 trally by the second segment. There are a few setae on the ventral edges 

 of all the segments. The second segment overlaps the first and third 

 and its ventral expansion is almost circular and without a spine. The 

 ventral edge of the third segment is rounded; this segment is very large; 

 its posterior border is almost regularly concave and meets the dorsal 

 convex (in posterior part), overhanging the fourth segment. The fourth 

 segment is not so deep as the third; its posterior border slopes first 

 anteriorly (straight) and then posteriorly (rounded) so producing a 

 ventro-posterior wing that ends in a spine which lies along the ventral 

 edge of the fifth segment. The fifth segment is much like the fourth in 

 shape, but is smaller with a ventro-posterior wing and spine. The sixth 

 segment is stout and short, its dorsal border is straight ; at the posterior 

 end is a well developed lateral spine. The dorsal border is longer than 

 the ventral due to a concavity of the ventro-posterior edge producing a 

 dorso-posterior wing ending in a small spine. 



