54 Proceedings of the Royal Physical Society. 



that the plan is quite the same, although the extent of the 

 groove-system is considerably diminished. 



The facial bones of Homosteus are extremely difficult of 

 determination, and I must frankly confess that I have come 

 to no certain conclusions regarding them. In the specimen 

 represented in PL III., Fig. 1, are three detached bones, A, B, and 

 c, on each side of the anterior part of the cranium, by which 

 B and c are also partly concealed, while on the right side the 

 bone A is seen only in longitudinal section, having stood on 

 edge to the bedding of the rock. When those bones are 

 seen in connection with examples of the buckler, they 

 always occur in the same order, and isolated specimens of 

 all of them are also in the collection of the Edinburgh 

 Museum. 



The bone A is broadest behind the middle, narrowest at 

 each end, especially the anterior one. In the specimen here 

 figured it is seen from the internal aspect, having apparently 

 got turned over; but other specimens show that on the 

 external aspect near the middle it had a patch of the usual 

 tuberculation, with a short lateral-line system gi-oove. This 

 bone is iigured by Hugh Miller as " lateral cerebral plate," 

 but as many specimens in the collection show that its 

 position was immediately below the edge of the antero- 

 lateral portion of the buckler external to the orbit, the 

 oTOOve on its surface beino- a continuation of the transverse 

 branch on the post-orbital, it is clearly the homologue of the 

 paddle-shaped bone or maxilla in Coccosteus (Fig. 3). If this 

 be the case, then we may assume that the bone B, following 

 and parallel to it, is the mandible ; but no traces of teeth 

 can be found on either, or, indeed, on any bone which it is 

 safe to refer to Homosteus. Like the Sturgeon, it must have 

 been edentulous. 



The bone c is figured by Hugh Miller ("Footprints," fig. 45a) 

 as a clavicle (here he meant what we now call post-clavical) ; 

 but, of course, such an interpretation founded on its super- 

 ficial resemblance to the post-clavical of a modern Teleostean 

 is here negatived by its position. Hugh Miller noticed the 

 tuberculation of the outer side of one of its extremities, but 

 in accordance with his theory of its position in the animal. 



