226 BULLETIN : MUSEUM OF COxMrAKATIVE ZOOLOGY. 



Fig. 5L Plati/somus circularis Newb. and Worth. Coal Measures; Mazon Creek, 

 Grundy County, Illinois. Complete fish with well-preserved fins and 

 squamation, X f- 



Fig. 52. Cheirodus orbicularis (Nevfh. and Worth.). Coal Measures; Mazon Creek, 

 Grundy County, Illinois. Complete fish with well-preserved fins and 

 dorsal and ventral peaks, X f- 



Fig. 53. Deltodus occidentalis Newb. and Worth, (var. D. latior Newb. and Worth ). 

 Keokuk limestone ; Keokuk, Iowa. Posterior dental plate referred to 

 right ramus of the lower jaw. 



Figs. 64, 54 a, 54 6. Helodus incisus, s-p. dov. Mississippian ; Salem, Indiana. Sup- 

 posed symphj'sial tooth corresponding to the form known as " Helodus 

 coxanus " Newb. Seen in anterior, posterior, and lateral aspects, 



X \. 



Fig. 55. Deltodus spatulatus Newb. and Worth. Burlington limestone ; Burling- 

 ton, Iowa. Anterior dental plate referred to the left ramus of tlie 

 lower jaw, and described by Messrs. St. Joim and Worthen as a 

 distinct species {" D. convolutus "), X f- 



Fig. 56, 56 a. Tuberculated dermal plate of an undetermined Elasmobranch. 

 Kinderhook limestone ; Burlington, Iowa. Tlie unsymmetrical cross- 

 section near the base is shown in Fig. 56 a, X j. 



Fig. 57. A spiniform dermal tubercle of the same nature as that shown in Fig. 

 56, the external surface much corroded and displaying the fibrous 

 internal structure, X j- 



Fig. 58. Homacanthus acinaciformis, sp. nov. Chemung Group ; Warren, Penn- 

 sylvania. Lateral aspect of spine lacking inserted portion, X \- 



Fig. 59. Hoinacmithus delicatulus, sp. nov. Kinderhook limestone ; Le Grand, 

 Iowa. The same spine as shown in Plate 3, Fig. 28, four times 

 enlarged. 



The originals of Figures 48, 51, and 52 are preserved in the Peabody Museum 

 of Yale University; the remainder in the Museum of Comparative Zoology. 



