PLATE i. 

 Photographs of Triarthrus bccki, made by C. E. Beecher. 



Fig. i. Specimen 213. The dorsal test has been removed from the glabella, reveal- 

 ing the outline of the posterior end of the hypostoma, the proximal ends of the antennules, 

 the gnathites, and incomplete endopodites of some appendages, x 5.43. 



Fig. 2. Specimen 214. The head of a complete large specimen. Part of the thorax 

 is shown on pi. 3, fig. 6. Note especially the form of the segments of the endopodites and 

 of the anterior coxopodite on the right side, x 7.33. 



Fig. 3. Specimen 217,. This specimen shows better than any other the form of the 

 gnathites of the cephalon. Note also the setae of the exopodites under the cheek at the right. 

 The appearance of a hook on the posterior gnathite on the right may be accidental, but it 

 does not show broken edges, x 6.85. 



Fig. 4. Specimen 215. The ventral side of the cephalon of a small entire specimen. 

 Shows well the form of some of the gnathites and a few of the endopodites. Note the 

 unusual position of the antennules. x 7.63. 



Fig. 5. Specimen 226. This specimen did not photograph well, but is important as 

 showing the exopodites and endopodites emerging from under the cephalon. x about 6. 



