352 Proceedings of the Royal Physical Society. 



by another plate, of which the right is larger, the left smaller 

 than itself. External to each of the latter is the remaining 

 plate of each side, of considerably larger size, of an irregularly 

 triangular shape, and placed between the posterior margin of 

 the squamosal and the post-temporal {'p.t), which latter it 

 largely overlaps. These are certainly the plates which in 

 other Ganoid fishes {Lepidosteus, Polypterus) have sometimes 

 been called " supra-occipitals " and " epiotics," but they are 

 mere scale-bones, and occupy the place of the supra-temporal 

 chain in Teleostei. 



A very distinct suhorhital bone (s.o., Fig. 5) is seen in a 

 large number of specimens.- It consist of two limbs — an 

 upper and longer vertical one meeting below at nearly a 

 right angle w^ith a shorter horizontal portion, the bone being 

 considerably expanded at the junction. Above, the suborbital 

 was suspended from the post-frontal region of the cranial 

 shield, — below, it comes in contact with the middle of the 

 maxilla. This suborbital is the bone wdiich Sir Philip 

 Egerton has interpreted as the " prsemaxilla " in his memoir. 



All these plates are externally marked with, pores, and 

 often with furrows and ridges radiating from the centres of 

 ossification ; often also the surface becomes corrugated, some- 

 times almost granulated ; but I have seen no positive traces 

 of ganoine upon the surface. 



Internal Ci^anial Pones. — There is a large parasphenoid 

 much resembling that of Acijjenser in shape ; but, unlike 

 Prof. Young, I can find no remains of ossification in the 

 chondrocranium, which can be described, or even relied upon 

 as being such. Although such ossifications may very likely 

 have existed, it seems very improbable that they attained 

 any considerable dimensions. 



Hyoid Arch. — The most easily recognised bone of the 

 entire head is the hyomandihular {h.m., Figs. 2 and 5), w^hich 

 passes from the squamosal region obliquely downwards and 

 backwards. It is shaped much as it is both in Acipenser 

 and Polyodon, being constricted in the middle and flattened 

 anteroposteriorly in its upper part, laterally in its lower. 

 In one specimen in the British Museum there is an appear- 

 ance as of an ossified symplectic, extending from the lower 



