SPECIMENS OF TRIARTHRUS. 157 



which really converge in an anterior direction. Between the ridges are shallow canoe-shaped 

 depressions, which have the appearance of areas for the insertion of muscles. 



Measurements: Length, 31 mm. ; width at back of head, 15 mm. ; distance, in a straight 

 line, from point of insertion of the right antennule to its tip, 14.25 mm.; it projects 12 mm. 

 beyond the cephalon. 



Specimen No. 218 (pi. 6, fig. 3; text fig. 43). 



This specimen is a large one, developed from the lower side, but retains only the endopo- 

 dites of a few appendages. The cephalon and anterior portion of the thorax are missing. 



Professor Beecher had a drawing made to show the appendages on the right-hand side 

 of the last two segments of the thorax, seen of course from the ventral side. This drawing 

 shows well the broadening of the basipodite, ischiopodite, and meropodite, while the coxopo- 

 dite is thick and heavy, and the inner end of the gnathobase somewhat rugose. Almost 



Fig. 43. Triarthrus 

 bccki Green. Drawing 

 to represent the writer's 

 interpretation of the ap- 

 pendages of specimen 

 218. Drawn by Miss 

 Wood. X 10. 



every segment of the endopodites has one or more pits for insertion of spines, these being 

 along the anterior or posterior margins. The exopodites lack the setae, but show no unusual 

 features. 



Specimen No. 222 (pi. 4, fig. 5). 

 Illustrated: Amer. Jour. Sci., vol. 47, 1894, pi. 7, fig. 3 (drawing). 



A small specimen, developed from the lower side, and used by Professor Beecher to 

 illustrate the form of the segments of the endopodites of the pygidium. In addition to this, 

 it shows very well the form of the endopodites of the thorax. All of the appendages on 

 the specimen are shifted to the left of their normal position. This specimen differs from 

 most of the others in that the segments of the endopodites do not lie with their greatest 

 width in the horizontal plane, but were embedded vertically, with the posterior edge down- 

 ward. From this circumstance they retain their natural shape, and it is seen that they are 

 naturally flattened, with about the same thickness in proportion to length and width as in 

 some of the modern isopods (Serolis, for instance). In even the most anterior of these 

 endopodites (that of the second segment) the ischiopodite, meropodite, and carpopodite are 



