PLATE XVI 



TAGK- 

 Fig. 1. A&TEKOFiYl'HIUS VETUSTUS, St. J. and W 435 



1 a. Side view, enlarged two diameters ; 1 b, section of one side further enlarged, showing 



details of intercostal striation, and appearance of the more or less worn poste- 

 rior denticles ; 1 c, enlargement of portion of posterior face, showing position of 

 denticles along the posterolateral angles, also the faint median ridge; 1 d, trans- 

 verse section, "enlarged. Lower fish-bed, Kiuderhook; Burlington, Iowa. 



Fig. 2. AsTEKorTYCHius Keokuk, St. ,T. and W 436 



2 a Side view of an imperfect spine, enlarged two diameters, and restored in outline ; 2 6, 



sketch of the j>osterior face, enlarged two diameters ; 2 c, transverse section. Keo- 

 kuk limestone ; 'Warsaw, Illinois 



Fig. 3, 4. Asteropti'ciuus St. Ludoyici, St. J. and W 437 



3 a Lateral view of a perfect preserved specimen, showing intercostal tuhercles, and poste- 



rior denticles — the latter are represented slightly too large — enlarged two diame- 

 ters ; 3 b, section of posterior face, enlarged two diameters: 3 c, d, side views of 

 denticles belonging to the upper aud lower series, enlarged ; 3 e, transverse section. 

 St. Louis limestone ; Alton. Illinois. 



4 a. Side view of a nearly entire fin-spine : 4 b. section of the posterior face near the lower 



extremity, enlarged one-half, showing median keel and position of denticles ; 4 c, 

 section along the anterior margin, enlarged, showing two costs, and striato -punc- 

 tate intercostal spaces : 4 d, en argement of section from the posterior border near 

 the lower extremity, showing the irregular striae in the intercostal spaces, and the 

 posterior denticles; 4 e, enlargement" of posterior border near upper extremity, 

 showing the downward hooked denticles, etc.; 4f.fi, transverse sections near the 

 lower and upper extremities, enlarged one-half, showing relative prominence of 

 median keel in different parts of the spine. Same horizon, St. Louis, Missouri. 



Fig. 5,0. Asteeopty cuius tenuis, St. J. and W 438 



5 a. Side view of a large, nearly entire spine ; 5 b, enlargement of a portion of the surface ; 



5 c ,transverse section near the lower extremity. Chester limestone, Chester, 111. 

 G a. Lateral view of a fragment showing the tip of a spine, enlarg d two diameters ; 6 b, 

 enlargement showing portion of the posterior face, which is faintly channeled in- 

 stead of keeled, as in" the lower portion of the spine ,• 6 c, enlargement of the pos- 

 terior border, showing intercostal siriation, and denticles; 6 d, transverse section, 

 enlarged two diameters. Same horizon and locality. 



Fig. 7. Asteroptychius BEL1ULUS, St. J. andW 439 



7 a . Side view of a small spine showing the base ; 7 b, view of antei ior edge ; 7 c, transverse 

 section j 7 d, enlargement of portion of lateral surface. Coal Measures ; Carlin- 

 villej Illinois. 



Fig. 8-11. Acondylacaxtiius GRACiLLis, St. J. and W 433 



S o . Side view of spine, enlarged one-half ; 8 b, transverse section. Upper fish-bed, Kinder- 

 hook; Burlington, Iowa. 



9 a. Side view of a fragment near the upper extremity, enlarged two diameters ; 9 6, poste- 

 rior face, enlarged two diameters,- 9 c, transverse section, enlarged. Same horizon 

 and locality. 



10 a. Side view of the tip of a very small spine, referred to the above form, enlarged two 



diameters ; 10 &, transverse section ; 10 c, enlargement of one of the denticles seen 

 from the outer side. Lower fish-bed, Kiuderhook ; Burlington, Iowa. 



11 ft. Lateral view of a fragment of a large spine, probably referable to this species, show- 



ing the surface iu perfect state of preservation ; 11 b, enlargement of a portion of 

 the surface, and profile section of the costie; 11 c, transverse section. Upper fish- 

 bed, Kiuderhook; Burlington, Iowa. 



Fig. 12,13. Acoxdylacanthus -equicostatus, St. J. and W 434 



12 a. Lateral view of a large spine ; 12 b, enlargement of a portion along the anterior margin ; 



12 o, enlargenient'showing section of "the posterior face, showing form of denticles, 

 etc; 12 d, side view of a denticle, enlarged; 12 e, transverse section ; 12/, enlarged sec- 

 tion of anterior portion of spine. Keokuk limestone ; Warsaw, Illinois. 



13 a. Side view of a smaller specimen; 13 &, enlargement showing the broad intercostal 



space a'ong the anterior margin ; 13 c, enlargement of portion along the posterior 

 border; 13 d, enlargement of the posterior face; 13 e, transverse section, enlarged.- 

 Same horizon, Keokuk, Iowa. 



Fig. 14. Axaclitacanthus semicostatus, St. J. and W 443 



14 a. Side view of spine; 14 b, transverse section near the broken distal end; 14 c, trans- 



verse section near the inferior extremity. Upper Burlington limestone; Burling- 

 ton. Iowa. 



