I 62 



THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. 



On the ventral side are a number of endopodites, but they are more fragmentary than 

 those of the other half of the specimen. Some of the exopodites are well shown, the blades 

 being in all cases broken from the shaft. Two of the endopodites of this specimen are of 

 especial interest, as they have interarticular membranes between the last three segments. 

 Professor Beecher made a drawing of one of these which he placed under his pen drawing 

 (text fig. 45). 



Measurements: The specimen is 5 mm. long from the front of the second thoracic 

 segment to the end of the pygidium. The setae on the exopodites of the anterior thoracic 

 segments are 1.7 mm. long, as exposed from the dorsal side. Some of those on the posterior 

 part of the pygidium, only incompletely exposed, are 0.31 mm. long. 



The dactylopodite of the first endopodite showing the articular membranes is 0.23 mm. 



\ 



Fig. 46. Crypolithus tessellatus Green. A part of a thorax and pygidium, 

 showing appendages. Drawn by Professor Beecher. Specimen 238. X 10. 



long and 0.13 mm. wide. The propodite is of the same length and 0.17 mm. wide. The 

 interarticular membrane between them is 0.066 mm. thick. The spines on the dactylopodite 

 of this appendage are 0.15 mm. long. All measurements were made on photographs. 



Specimen No. 238 (pi. 8, fig. 4; text fig. 46). 



A triangular specimen consisting of the greater part of a pygidium and parts of all the 

 thoracic segments. Under the thorax the specimen has been so cleaned that the outer por- 

 tions of the endopodites are well shown, while under the pygidium the greater part of the 

 endopodites seem to have been removed, disclosing the sete of the exopodites. As in other 

 specimens, the endopodites of the thorax turn backward at the distal end of the carpopo- 

 dite, which is broad and curved, and bears a tuft of spines on the posterior margin. The 

 dactylopodites seem to preserve their natural shape, and are very nearly cylindrical in form. 

 Under the pygidium are several sets of overlapping fringes of setae of exopodites, and along 

 the edge of the dorsal furrow, a number of fragments of segments of what may be coxopo- 

 dites while with them are a number of fragmentary shaft of exopodites. 



Measurements: The pygidium is 3.3 mm. long, the thorax 3 mm. 



