^"^I'ml' ] PROCEEDINGS OF THE NATIONAL MUSEUM. 451 



jjfiuul tube sends a braiicli lateially to the external aM.i;le of the skull in 

 all the genera mentioned, except in iMaeroi)etalichthys, where this 

 point can not be demonstrated in my specimen, owiny; to tlie loss of the 

 border. Still more anteriorly on the i)ostorbital bone it diverges again, 

 sending a short branch in ward and one forwards in Coccosteus ami Ti- 

 tanichthys. In JUnichtiiys icrreUii it <loes not divide, bnteontinues, aud 

 joins the lateral tube of the lyra. In both Coccosteus and IMacropetal- 

 ichthys the transverse branch extemls towards tin' middle line. In 

 the former it unites with that of the O[)i)osite side, and forms at its 

 middle portion, the posterior border of the lyra. In i\Iacropetalichthys 

 t)n the other hand, it Joins the posterior tube at an angle well behind 

 the extremity of the lyra as already described. Thus the last-named 

 genus resembles Coccosteus in this one point more than it does any 

 of the other Arthrodira. (Fig. C.) 



The cranial segments discernible are as follows. They may be readily 

 traced on the specimen, since the sculptured surface and indeed the 

 greater })art of the bone-substances have disappeared, and the cast of 

 the inferior surface is distinctly preserved. This surface, is however, 

 wanting from most of the top of the muzzle, so that the relations of the 

 ethmoid elements cannot be uuideout. From the middleof the superior 

 border of the orbits forwards extends an element which is prefrontal or 

 frontal ; but which one the injury to the top of the muzzle does not per- 

 mit me to determine. It extends down on each side of the muzzle in 

 front of the orbit. At the anterior border of the latter, it is pierced 

 n[)wards an<l forwards by a deep iH)tch like groove which receives a 

 corres[)on(ling wedgelike auterosui)erior extremity of the element 

 which I call provisionally the jugal or malar element. This bone ex- 

 tends below and behind the orbit, containing in the latter region a 

 center of radiating ossification. The median or (:') frontoi>arietal ele- 

 ment encroaches on the merlian element of the top of the muzzle as 

 far forwards as oi)i)osite the middle of the orbits by a convex anterior 

 border. Its ossification radiates from the junction of the lateral 

 branches of the lyra, in all directions, and, while its anterior and lateral 

 i)orders are easily discernible, its posterior ones are not so clear. It 

 probably extends to a point half way between its anterior border an<l 

 the posterior border of the head-shield. The posterior section of the 

 prefrontal extends oblicpu'ly backwards and is succeede<l by a wide 

 longitudinally oval element, which from its position might be termed a 

 postfrontal, although it includes within itself the region of the i)ostor- 

 bital. Posterior to it is a subdiscoid element of similar size, and a little 

 wider than long, which is in the position of the supratemi)oral element 

 of the Stegocei)]ialous skull. Its center is the point of divergence of 

 three tubes already described, and its ossilication radiates from the 

 same point. Exterior to' this element and the one iji front of it, and 

 Joining the posterior face of the malar is a large area in the position 

 of the Stegocephalous squamosal element. Ossification radiates from 



