NEOLENUS. 27 



Measurements: The pygidium is 19 mm. long (without the spines) and about 34 mm. 

 wide at the front. The exopodites show faintly beneath the pygidial shield, but their proxi- 

 mal ends are too indistinct to allow accurate measurement. Apparently they were just 

 about long enough to reach to the margin of the shield. The best preserved one, that of 

 the second segment in the pygidium, is about u mm. long, 2.5 mm. wide at the widest; 

 the distal lobe is 2.5 mm. long, and the longest seta: of the main lobe 3.5 mm. long. The 

 pleural lobe of the pygidium is just 1 1 mm. wide at this point. 



The endopodites project from 8 to 12 mm. beyond the pygidium, showing about four 



segments. 



The thoracic exopodite described above is n mm. long and 2.75 mm. wide at the widest 

 part. The distal lobe is 3.5 mm. long and 2.25 mm. wide, and the longest setae on the main 



lobe 3 mm. long. 



Specimen No. 65519. 



Illustrated: Walcott, Zittel-Eastman Text-book of Paleontology, vol. I, 1913, fig. 1343; Smithson. Misc. 

 Coll., vol. 67, 1918, pi. 21, fig. 6. 



This specimen is somewhat difficult to study but is very valuable as showing the natural 

 position of the exopodites of the anterior part of the thorax. Walcott's figures are excel- 

 lent and show the broad leaf-like shafts, the distal lobes with the re-entrant angles in the pos- 

 terior margin, and the long fine set;e of the main lobes. None of the distal lobes retains its 

 setae. All extend back to the dorsal furrows, but the proximal ends are not actually shown. 



The specimen is especially important because it shows the same distal lobes as speci- 

 men No. 65514, and demonstrates that they are a part of the exopodite and not of any other 

 structure. 



Measurements: The exopodite belonging to the fourth thoracic segment is 23 mm. 

 long and 4 mm. wide at the widest part. The longest setae are 7 mm. in length. 



Specimen No. 65520. 

 Illustrated: Walcott, Smithson. Misc. Coll., vol. 67, 1918, pi. 20, fig. 2; pi. 22, fig. I. 



This is a practically entire specimen, on two blocks, one showing the interior of the shell, 

 and the other the one figured by Walcott, a cast of the interior. The first shows the low 

 rounded appendifers at the anterior angle of each axial tergite. They are almost entirely 

 beneath the dorsal furrows and do not project so far into the axial lobe as those of Ccraurus 

 and Calynicnc. In fact, only those at the anterior end of the thorax project inward at all. 

 As expected, there are five pairs on the pygidium. The cephalon is unfortunately so exfol- 

 iated that the appendifers there are not preserved. The doublure of the pygidium is ex- 

 tremely narrow. 



The cast of the interior shows, rather faintly, the exopodites of the right side of the 

 thorax and of the left side of the cephalon, and, still more faintly, the caudal rami and 

 a few pygidial endopodites. The exopodites on the right side are in what seems to be the 

 customary position, directed obliquely forward and out\vard, and the tips of their distal 

 lobes project slightly beyond the edge of the test. These lobes were interpreted by Walcott 

 as epipodites, but after comparing them with the terminal lobes of the exopodites of speci- 

 mens No. 65519 and 65514 I think there can be no doubt that they represent the same 

 structure. The pleura of the individual thoracic segments on this side of the specimen 

 have an unusual appearance, for they are bluntly rounded or obtusely pointed, instead of 

 being spinose. 



