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Notes on Acanthodian Sharks 
other hand, it is very probable that they. could not have altered quickly 
their direction, speed, or plane of movement, and they would thus be 
placed at a serious disadvantage when competing with ganoids, dipnoans, 
even with other sharks, for the capture of varied forms of prey. So, 
also, the teeth of Acanthodians indicate a smaller range for functional 
adaptation than the dentition of other sharks. Finally, the elaborate 
specializations of the integumentary defenses of Acanthodians lead in 
the direction of enlarging individual dermal cusps, instead of that of 
fusing the bases of the cusps. And the result was an unfavorable one. 
For the limit of the size of the individual cusp could soon be reached, 
while that of the fused basal plate (a true membrane bone) was greater 
and more plastic. Even the most perfectly armored Acanthodian, there- 
fore, could not compete in this regard with the contemporary ganoids. 
DESCRIPTION OF FIGURES. 
Fies. 1-11. Teeth of Acanthodians. Figures of Ischnacanthus, excepting 
Fig. 11, which is of Acanthodopsis wardi. 
Fic. 12. Jaw and brancnial arches of Acanthodes bronni. 13. Jaw arches 
of Ischnacanthus gracilis. 14. Head-roof of Climatius scutiger. 15. Detail of 
a shagreen denticle from the head-roof of Climatius reticulatus. 16. Neural 
and hemal arches of Ischnacanthus gracilis. 17. Neural arches and dorsal 
fin, ibid. 18. Pectoral spines and girdle of Climatius reticulatus. 19. Pectoral 
and pelvic girdles and spines of Diplacanthus striatus. 
Fias. 20-27. Fins and related structures in Acanthodians. 20. Parexws 
falcatus. 21. Ibid. 22. Caudal of Diplacanthus tenuistriatus. 23. Second 
dorsal of Euthacanthus macnicoli. 24. Dorsal of Climatius wncinatus. 25. 
Caudal of Acanthodes bronni. 26. Detached spine of Climatius reticulatus. 
27. Shoulder girdle (half) of Climatius falcatus, showing dermal elements. 
Fics. 28-36. Sensory structures in Acanthodians. 28, 29. Acanthodes bronni. 
30. Climatius grandis. 31, 32. Ischnacanthus gracilis. 33. Climatius. Detail 
of lateral line at a point anterior to second dorsal fin. 34. Huthacanthus ele- 
gans. Lateral line. 34a. Detail of a shagreen denticle margining lateral 
line. 35. Acanthodes bronni. Detail of lateral line. 386. Huthacanthus macni- 
coli. Detail of enlarged scales of ventral body-wall. 
