CERAURUS. 6 1 



form of the exopodites could not be made out. The shaft was apparently rather short, unseg- 

 mented, and fairly broad. The setae appear from the sections to have been more or less 

 blade-shaped and to have overlapped, as do those of the exopodites of Cryptolithus. Judg- 

 ing from their position in the sections, the setae not only bordered the posterior side of the 

 shaft, but radiated out from the end as well. 



The pygidium shows three pairs of functional appendifers, hence three pairs of appen- 

 dages have been supplied. There is a fourth pair of rudimentary appendifers, but as they 

 are beneath the doublure they could not have borne ambulatory appendages. 



THE APPENDAGES OF ACIDASPIS TRENTONENSIS WALCOTT. 

 (PI. 6, fig. 6.) 



A single individual of Acidaspis trentonensis, obtained from the same locality and hori- 

 zon as the specimens of Triarthrus and Cryptolithus, when cleaned from the ventral side 

 shows a number of poorly preserved endopodites which seem very similar in shape and 

 position to those of Triarthrus. One endopodite on the right side of the head and the first 

 five on the right side of the thorax are the best shown. All are slender, are directed first 

 forward at an angle of about 45 with the axis, then, except in the case of the cephalic 

 appendage, turn backward on a gentle curve and extend a little distance beyond the margin 

 of the test, but not as far as the tips of the lateral spines of the thoracic segments. 



The individual segments of the endopodites can not be seen clearly enough to make 

 any measurements. On the fourth and fifth endopodites of the thorax, some of the seg- 

 ments seem to be broad and triangular as in Triarthrus. All that can be seen indicates that 

 Acidaspis had appendages entirely similar to those of Triarthrus, but perhaps not quite 

 so long, as they seem not to have projected beyond the limits of the lateral spines. There 

 are no traces of antennules nor, unfortunately, of exopodites. 



Measurements: Length 8 mm. 



Walcott (1881, p. 206) stated that his sections had shown the presence in this species 

 of legs "both cephalic and thoracic" and also the "spiral branchiae." His specimens were 

 from the Trenton at Trenton Falls, New York. 



THE APPENDAGES OF CRYPTOLITHUS. 



Cryptolithus tessellatus Green. 

 (PI. 6, fig. 7; pis. 7-9; text figs. 20, 25, 45, 46.) 



(See also Part IV.) 

 Illustrated: Beecher, Amer. Jour. Sci., vol. 49, 1895, pi. 3. 



When Professor Beecher wrote his short article on the "Structure and Appendages of 

 Trinucleus" (1895), he had only three specimens showing appendages. In his later work 

 he cleaned several more, so that there are now thirteen specimens of Trinucleus = Cryp- 

 tolithus available for study, though some of these do not show much detail. In his last 

 and unpublished study, Beecher devoted the major part of his attention to this genus, and 

 summarized his findings in the drawings which he himself made of the best individuals (text 

 figs. 45, 46). Valiant (1901) stated that he had found a Trinucleus with antennae in the 

 Frankfort shale south of Rome, New York. The specimen has not been figured. 



