IOWA ACADEMY OP SCIENCES. 
193 
Lepidechinus is manifestly closely related to Archaoocidaris 
and the generic separation of the two appears to rest chiefly on 
the imbricated character of the plates on the former genus. To 
what extent this feature may be relied upon as a generic char- 
acter cannot at this time be stated. Certain forms of Archseo- 
cidaris appear to have beveled interambulacral ossicles and this 
may prove to be one of the distinctive features of the genus. 
Meek has also noted this fact in connection with several species 
belonging to the latter group. 
Lepidechinus squamosus (Meek & Worthen). 
Eocidaris squamosus Meek & Worthen, 1869; Proc. Acad. Nat. 
Sci. Phila., vol. XXI, p. 79. 
Eocidaris squamosus Meek & Worthen, 1873; Geol. Sur. Illinois, 
vol. V, p. 478, pi. ix, flgs. l^a-g. 
Lepidocidaris squamosus Meek & Worthen, 1873; Geol. Sur. Illi- 
nis, vol. V, p. 482. 
Similar to A. sUumardi, but with interambulacral plates bev- 
eled so as to allow marked imbrication; and ambulacral ossicles 
much more irregular. 
Horizon and localities. Lower Carboniferous, Burlington 
limestone: Burlington, Iowa. 
Plate xviii. 
Figure 1. 
la. 
lb. 
l c. 
Figure 2. 
2a. 
2h. 
Figure 3. 
Figure 4. 
4a. 
lb. 
Figure 5. 
Figure 6. 
Plate xix. 
Figure 1. 
la. 
lb. 
EXPLANATION OP PLATES. 
Archseocidaris biangulata. 
Side view of spine. 
View of same from below. 
Interambulacral plate. 
Archasocidaris megastylus. 
Spines and plates. 
Cross-section of Interambulacral plate. 
Archasocidaris aculeata. 
Oligoporus mutatus. 
Type specimen. 
Ambulacral plates (enlarged). 
Archasocidaris agassizi. 
Spines and plates. 
Archasocidaris dininnii. 
Alelonites multipora. 
Side view of nearly perfect specimen. 
Same from above. 
