EXPLANATION OF PLATE VIII. 



Fig. 1. Pi;ODUcrus sicmii;kticulatijS var. Iviosii. (.Pnno 111.) 



a. Ventral view of .specimen of ordinary size. 



1>. Lateral view oflliesanie. 



c. Dorsal view of a typical example of /'. scminiicuhiliis from Soiitl cru Iowa; introtlaccd for 

 comparison. 

 Fig. 2. PiioDjJCTL's costatus. (Pago 109.) 



a. Ventral view of a typical example of the American form of this species. 



6. Dorsal view of tbo same. 



c. Ventral view of another example. 



ct. Lateral view of the same. 

 Fig. 3. Pr.oDUCTUS Nkbi:ascensis. (Pago 110.) 



a. Typical example from Nebraska, ventral view. The spines arc represented a little too 



coarse in the fignres. 



b. Dorsal view of the same. 



c. Partially-exfoliated example from near Santa F(S. 



d. Lateral view of the same. 

 Fig. 4. Pi:oductus MtiiticiTCS. (Page 120.) 



a. Ventral view of a partially-exfoliated example. 



h. Posterior view of the same. 



c. Lateral view of the same. 

 Fig. 5. Productus longispixus. (Page 118.) 



a. Ventral view of a typical form of the American shell. 



h. Dorsal view of the same. 



c. Ventral view of a variety from ne.-ir Santa F<S. 



(I, Dorsal view of the same. 

 Fig. 6. PitODUCTUs Mexicanus. (Page 120.) 



a. Ventral view of a specimen from Nevada. 



1). Lateral view of the same. 



c. Posterior view of the same. 



