i6o 



THE APPENDAGES, ANATOMY, AND RELATIONS OF TRILOBITES. 



The exopodites and endopodites of the left side of the thorax are best preserved. The 

 exopodites are above the endopodites, and only that portion exposed from the ventral side 

 which projects beyond the line at which the endopodites bend backward. The endopodite 

 on the left side of the first thoracic segment is the best preserved. It shows seven segments, 

 the outer ones best. The coxopodite is short and narrow, the basipodite somewhat heavier 

 and longer, while the carpopodite and propodite are the widest and strongest segments. The 

 propodite is triangular and flattened, like the segments on the middle and posterior part of 

 the thorax of Triarthrus. At the inner end of the ischiopodite and meropodite are tufts of 

 spines pointing inward and backward. These are not shown on any of the photographs, 

 but may be seen with the light striking the specimen at the proper angle. 



It is not possible to count the exact number of limbs, but one gets the impression that 

 on the left side of this specimen there are twenty-one sets of appendages, six of which of 

 course belong to the thorax. On the thorax and anterior part of the pygidium, successive 

 endopodites show the propodites and dactylopodites becoming progressively more slender and 

 shorter, while the ischiopodites, meropodites and carpopodites become shorter and more tri- 

 angular, and with increasingly large numbers of short spines on their posterior borders. Back 

 of the fourth endopodite on the pygidium it is not possible to make out the detail, but the 

 appearance is of an endopodite consisting of short broad segments fringed at the back with 

 short spines, the ones at the very posterior end appearing to be exceedingly short and rudi- 

 mentary. 



The exopodites are not so well shown as in some others but the setae are flattened and 

 blade-shaped, and often bear numerous small spines. 



Measurements: Length (lacking most of the fringe), 10.5 mm. Width of thorax, 

 10.5 mm. Length of hypostome, 1.41 mm., width at front, 1.46 mm. The distance from 

 back of fringe to end of antennules is 5.4 mm. If straightened out, the left antennule 

 would be about 6.1 mm. long. In the first 3.1 mm., there are only ten segments, so that the 

 average length of a segment is 0.31 mm. The distance from the inner end of the endo- 

 base of the first segment of the thorax to the outer end of the meropodite is 2,43 mm., and 

 from that point to the end of the dactylopodite 2.47 mm. making the total length 4.90 mm. 

 These measurements are taken from the photograph. Measurements taken from Professor 

 Beecher's drawing, which was made with the camera lucida, give a total length of 4.57 mm., 

 the distance to the outer end of the meropodite being 2.3 mm. and thence to the tip of the 

 dactylopodite 2.27 mm. Detailed measurements of the segments, on the photograph, are as 

 follows: coxopodite, 0.321 mm. ; basipodite, 0.78 mm. ; ischiopodite, 0.68 mm. ; meropodite, 

 0.642 mm.; carpopodite, 0.642 mm.; propodite, i.oi mm., dactylopodite, 0.825 mm. 



Illustrated 



, . . , . ., , . 



Specimen No. 235 (pi. 7, fig. 2; pi. 8, fig. 3; pi. 9, figs, i, 2). 

 : Amer. Jour. Sci., vol. 49, 1895, pi. 3, figs. 5, 6. 



Specimens 235 and 236 were originally parts of an entire Cryptolithus, but, as 

 Professor Beecher has explained, the specimen was cut in two longitudinally on the median 

 line, and the halves transversely just back of the cephalon, so that each now represents one 

 half of a thorax and pygidium. Both halves have been cleaned from both upper and lower 

 side, a perfectly marvelous piece of work, for the thickness is no greater than that of a 

 thin sheet of paper, and the soft shale of the matrix has a very slight cohesive power. 



Both sides of specimen 235 were figured, but the dorsal side was apparently then some- 



