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PROCEEDINOS OF THE NATIONAL MUSEUM. 



VOL. XXXIII. 



is the end vieAV of the U-shaped ridge and resulting central concavity 

 formed by the extension of the petaloid sectors of the basals onto the 

 infrabasals, as shown in fig. 8. The ventral (upper) end of the circlet 

 of infrabasals is, in common with the adjoining surface of the basals, 

 more or less honeycombed and disintegrated, but this condition does 

 not extend very far down; most of the infrabasals is 

 as solid in structure as the basals, and, so far from being 

 degenerate, they are remarkably well developed, when 

 the very large size of the basals in the specimens dis- 

 sected is considered. 



A ventral view (fig. 7) shows that the edges of the 

 infrabasals are sharp and clear-cut, and the sutures very 

 distinct; the outer sides are raised into a sharp angle; 

 the ventral surface is somewhat rough and irregular, 

 while the central canal is comparatively small, and 

 quinquelobate. 



The dorsal view (fig. 8) does not differ from that figured for the in- 

 frabasals of M. i^otundus (fig. 3). The surface, while smooth, is 

 raised into U-shaped ridges, forming an inward extension of the 

 ridges on the basals, the outer edges are rounded, and the central 

 canal is much larger than in the ventral view, and is round. 



Fig. 8.— Dorsal 

 view of iso- 

 lated infra- 

 basals of 

 Metaceinus 

 superbus. 



