Remains of the Pycnodont Fish, Mesturus. 5 



of the frontals and filling the re-entering angle in the anterior 

 margin of the supraoccipital is bilaterally symmetrical, 

 acutely pointed behind, and widest in front. Some of its 

 median tuberculations are relatively very small. The eth- 

 moidal and facial region in advance of the frontals is appa- 

 rently completely covered with irregular polygonal plates 

 (eth.), more finely tuberculated than the hinder portion of the 

 cranial roof. Some of the posterior median ethmoidal plates 

 are fused together, but indications of the original sutures are 

 distinct. The vomerine region (v.), as usual in Pycnodonts, 

 is shown to be very robust and provided with a regularly 

 arranged pavement of teeth. Remains of an external tuber- 

 culated plate on the right side may perhaps represent the 

 maxilla (PI. I. fig. 1, y). The stout smooth premaxillee 

 (pmx.) 7 each exhibiting the bases of three large teeth, are 

 preserved at the end of the snout. 



Specimen no. 24 (Leeds Catalogue). — The second well- 

 preserved specimen (PI. II.) wants the ethmoidal region, but 

 displays the greater part of the cranial roof behind, especially 

 on the right side. The supraoccipital plate (s.occ.) extends, 

 as described before, in a short pointed process fitting into the 

 large median supi-atemporal ; but it differs in being much 

 further produced forwards, and may, indeed, be regarded as 

 the supraoccipital proper fused completely with the proble- 

 matical median plate (p.eth.), which is a separate element in 

 the above-described fossil. The frontals (//•.) are apparently 

 similar in general form and proportions to those already 

 described; but there is a marked difference in the circum- 

 stance that they do not meet at any point in the middle line. 

 The supposed compound supraoccipital plate gradually con- 

 tracts in width in its anterior half, but is prevented by 

 truncation from ending quite in a point. Its contracting 

 lateral margins articulate with the frontals ; but its short 

 front border is apposed to another median plate (eth.) } which 

 extends as far forwards as the ethmoidal tesserae. This 

 element is also antero-posteriorly elongated, but gradually 

 widens to the foremost point of its suture with the frontals, 

 and is then quickly narrowed again at its irregular articula- 

 tion in front. It is doubtless equivalent to the triangular 

 portion of the ethmoidal shield, which only extends into the 

 frontal region for a very short distance in specimen no. 1. 

 The outlines of two of the polygonal ethmoidal plates can be 

 distinguished on the right side of the fossil immediately in 

 advance of the frontal. Among inner bones the crushed 

 ossified mesethmoid can be seen supporting the single denti- 

 gerous vomer, while a portion of the parasphenoid splint is 



