3O THE APPENDAGES, ANATOMY, AND RKI.ATIONS OF TKTLOBITES. 



crushed specimen. No. 2 is 10 mm. long and 6 mm. wide at the widest point. No. i is 

 5 mrn. long and 3.5 mm. wide. 



The crucial point in this determination is whether 2 and i are parts of the same appen- 

 dage. I believe they are, but others may differ. 



Specimen No. 65513. 

 Illustrated: Walcott, Smithson. Misc. Coll., vol. 57, 1912, pi. 45, fig. 3; Ibid., vol. 67, 1918, pi. 16, figs, i, 2. 



This is nearly all of the right half of an entire specimen, but the only appendages of 

 any interest are those of the cephalon. Five endopodites emerge from beneath that shield, 

 but as all are displaced it is not possible to say how many belong to the head. When held 

 at the proper angle to the light, the second and third from the front show faintly the par- 

 tial outlines of the coxopodites. The anterior side and end of the best preserved one 

 shows irregular stout spines of unequal sizes, and the inner end is truncated obliquely (fig. 

 6). These coxopodites are like those on the thorax of specimen No. 58589, but shorter 

 and wider. This of course suggests that the "exite" No. 2 of specimen No. 65515 may 

 be a cephalic coxopodite. The endopodite of this appendage, like the others on this cepha- 

 lon, is shorter and stouter than the thoracic or pygidial endopodites of the others described. 



Fig. 7. A restored section across the thorax of Neolcnus 

 scrratus, showing the probable form of attachment of the ap- 

 pendages, their relation to the ventral membrane, and the jaw- 

 like endobases of the coxopodites. 



Measurements: The cephalon is 24 mm. long and about 60 mm. wide. The coxopodite 

 of the third appendage is about 10 mm. long and 5.5 mm. wide at the widest point. The 

 corresponding endopodite is 19 mm. long and projects n mm. beyond the margin, which is 

 about 5 mm. further than it would project were the appendage restored to its proper position. 



RESTORATION OF NEOLENUS. 



(Text fig.. 7, 8.) 



This restoration is based upon the information obtained from the studies which have 

 been detailed in the preceding pages, and differs materially from that presented by Doctor 

 Walcott. The appendages are not shown in their natural positions, but as if flattened nearly 

 into a horizontal plane. The metastoma is added without any evidence for its former 

 presence. 



The striking features of the appendages are the broad unsegmented exopodites which 

 point forward all along the body, and the strong endopodites, which show practically no 

 regional modification. Although the exopodites have a form which is especially adapted 

 for use in swimming, their position is such as to indicate that they were not so used. The 

 stout endopodites, on the other hand, probably performed the double function of natatory 

 and ambulatory legs. 



