I 54 THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. 



are nearly cylindrical, but the ischiopodites and meropodites of several of the endopodites 

 show rather deep longitudinal grooves which appear to be rather the result of the shrinkage 

 of the thin test than natural conformations. 



The endopodites on the left-hand side have a number of short, sharp, movable, hair- 

 like spines, and cup-shaped depressions which are the points of insertion of others. On 

 the distal end of the carpopoclite of the first thoracic segment there seems to have been a 

 spine, whose place is now shown by a pit. This same endopodite shows, rather indistinctly, 

 three pits in the groove of the carpopodite, and the propodite has two. On the endopodite 

 of the second appendage on this side, both the carpopodite and propodite possess a fine hair- 

 like articulated spine at the distal end, that of the propodite arising on the dorsal and 

 that of the carpopodite on the posterior side. On the dorsal side of the carpopodite there 

 are three pits for the articulation of spines, and on the propodite, one. 



The exopodites belonging to the thoracic segments are of equal length with the endopo- 

 dites, and while the proximal portion of each is stouter than that of the corresponding 

 endopodite, the exopodites taper to a hair-like termination, while the endopodites remain 

 fairly stout to the distal segment. Most of the setae of the exopodites have been removed, 

 so that each remains as a curving, many-segmented organ, transversely striated, with a con- 

 tinuous groove along the posterior side. The setae appear to be set in this groove, one for 

 each of the transverse ridges on the shaft. 



A good deal of the test has been cut away on the left-hand side from the thorax and 

 pygidium, and the appendages exposed from above. Enough of the dorsal shell has been 

 cut away so that the anal opening is exposed, and directly behind the pygidium, on the 

 median line, is a bilaterally symmetrical plate with serrated edges which appears to be the 

 appendage of the anal segment. (See pi. 3, fig. 4.) 



Measurements: The specimen is 17 mm. long, and 8 mm. in greatest width (at the back 

 of the cephalon). From the median tubercle to the outer edge of the pleuron of the second 

 thoracic segment the distance is 3.7 mm. From the point of articulation to the distal end 

 of the spines on the dactylopodite of the second endopodite on the right-hand side is 4.3 mm. 

 The basipodite of this appendage is 1.5 mm. long, the ischiopodite i mm. long, the meropo- 

 dite 1.2 mm. Jong, the carpopodite 0.5 mm. long, the propodite 0.35 long, and the dactylopo- 

 dite 0.15 mm. long. On the left-hand side the endopodite of the first segment projects 

 3 mm. beyond the pleuron, the second, 3.2 mm. At the back the appendages extend a 

 maximum distance of 2.5 mm. behind the pygidium. The median spinose process of the 

 anal segment extends 0.75 mm. behind the pygidium, and is 1.6 mm. in greatest width. 



Specimen No. 204 (pi. 3, fig. i ; pi. 4, fig. 6; text fig. 42). 

 Illustrated: Amer. Jour. Sci., vol. 13, 1902, pi. 2, figs. 4, 5 (reproduced from photographs). 



This specimen, which is developed from the dorsal surface, shows especially well nine 

 appendages of the left side. The first represent the last segment of the cephalon; the re- 

 mainder belong to the thorax. As is usual, the exopodites of these appendages overlie and 

 curve behind the endopodites. All the exopodites have lost their setae and the segments of 

 the endopodites are flattened by crushing. The endopodites, while retaining only one or two 

 of the movable spines, have the cup-like bases of from two to four on each of the visible 

 segments, namely, the meropodite, carpopodite, propodite, and, in one case, the dactylopo- 

 dite. These appendages, although really marvellous in preservation, are of such small size 

 and react so badly to light that their study is very difficult, and Professor Beecher, who had 



