PLATE 4. 

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



Fig. i. Specimen 201. Another photograph, similar to fig. 4, pi. 3, but showing more 

 clearly some details of spines on the endopodites. x 12.66. 



Fig. 2. Specimen 201. Three appendages on the right side of the thorax. See also 

 pi. 2, fig. i and pi. 3, fig. 4. x 12.66. 



Fig. 3. Specimen 223. A small crushed specimen which nevertheless shows well the 

 appendages of the right side of the thorax, developed from the ventral side. Note coxopo- 

 dites, exopodites, and endopodites, and that all appendages are moved equally laterally from 

 their original position, x 11.4. 



Fig. 4. Specimen 219. Another photograph, with different lighting, of the individual 

 shown in pi. 2, fig. 6. This print brings out better the coxopodites and the folds of the 

 ventral membrane, x 3.23. 



Fig. 5. Specimen 222. This specimen is interesting, because it shows the endopodites 

 in what is probably their natural position, that is, in a plane nearly vertical to the plane 

 of the body, instead of being flattened down, as is usually the case. The appendages under 

 the pygidium are unusually well preserved, x 12. 



Fig. 6. Specimen 204. Photograph of the entire specimen of which a part is shown 

 in text fig. 42 and pi. 3, fig. i. X4_5. 



