BUFPALO SOCIETY OF NATURAL SCIENCES 



41 



Sclerotic ring (fig. ii). — A feature of great interest in this specimen 

 is the preservation of a complete sclerotic ring, situated near the right 

 orbit, and not far removed from its natural position. It is of great 

 importance as affording for the first time a correct idea of the form of 

 the eye in Dinichthys. 



Complete sclerotic rings of Arthrodira are extremely rare, owing to 

 the fact that on dissolution of the animal the segments composing the 

 ring became more or less disarranged and usually drifted apart. The 

 most perfect example of an arthrodiran sclerotic ring hitherto known 

 is the one belonging to the type specimen of Trachosteus, which 

 was figured by Newberry {Paleoz. Fishes N. Amer., PI. xlii, fig. 2). 

 It consists of four segments of very thin bone united by wavy sutures 

 so as to form a ring. 



Fig. II. Dinichthys magnificus, n. sp. Sclerotic Ring, Natural Size. 



Margin Restored 



Lowes 



In the present instance the sclerotic ring is not flattened down but 

 preserves much of its original outward convexity, this convexity 

 representing the configuration of the eyeball, which we thus learn was 

 spherical as in other vertebrates. The ring is composed of four seg- 

 ments; and the opening in the centre, corresponding to the eye 

 proper, is not round but ovate, with the narrow ends drawn out to 

 points. Its form is thus proved to have been much like that of 

 sharks and many other fishes. 



The sclerotic ring measures 50 mm. in width, and 11 mm. in height. 

 The eye opening is 20 mm. in long diameter (measured at the lateral 

 angles), and 15 in greatest width. 



Mandible. — Only the left mandible is preserved, and this lacks the 

 hinder third. Its form is well shown in the photograph reproduced in 



