NOTES ON PALEOZOIC CRUSTACEANS 91 



becomes increasingly pronounced, so that tlie pleurae of the last, 

 or I'Oth segment are almost parallel to the telson, and: their long 

 tapering margins nearly prevent contact at any point with those of 

 segment 9. Segments 1-5 bear an oblique groove or line on each 

 pleura, euggestive of, and probably homologous with the similar 

 grooves on the pleurae of the trilobites. These fine oblique 

 grooves are in every case situated very near the posterior margin 

 of the pleurae. The sixth and seventh segments, and all behind 

 them, fail to show these lines. On the other hand, in both the 

 entire specimens observed these segments, 6 and 7, are very 

 <closely juxtaposedi and present the appearance of being in a cer- 

 tain degree coalesced, the extremities being free for a less dis- 

 tance than is the case with the immediately preceding or succeed- 

 ing segments. From here backwards also the segments make an 

 abrupt turn in their direction, and begin to approximate parallel- 

 ism with the telson. 



There is herein good reason for deducing another homology 

 with the trilohites, as if in this probable partial coalescence of 

 the sixth and seventh segments were the beginning of the 

 pygidium, none of the pleurae of the segments from 5 downw'ard 

 bearing the oblique grooves. It may be noted that, where this 

 apparent coalescence of the pleurae manifests itself, the segments 

 •on the axis become narrower and the most marked incurvature 

 of the dorsal furrows begins. The caudal spine or telson is added 

 to the 10th segment without expansion at its base, is short, 

 rather blunt at its end and is ridged medially. 



Dimeiisions. The best preserved of all the specimens of this 

 crustacean is 24 mm long^ its head is 9 mm in median length, 

 and to the end of the genal spines, 12 mm. Width of head, 13 

 mm; width of abdomen 11.5; width of axis 5; length of telson 5. 



As an assurance of profound appreciation, of his generous and 

 stimulating attitude toward scientific investigation and his en- 

 thusiastic interest in the works of nature, and by his permis^ 

 sion, I have embraced the privilege of attaching to this ancient 

 and eurious denizen of our New York waters the name of 

 Theodore Roosevelt, vice-president of the United States and re- 

 cently governor of the state of New York. 



