SKELETON OF LEPIDOSTEUS. 



453 



each side a posterior temporal fossa roofed by the epiotic and 

 pterotic. Exoccipitals are as in Lepidosteics, but the upper wings 

 of the basioceipital in that genus are represented in Amico by two 

 or three pairs of bones, generally interpreted as the neural arches 

 of centra incorporated in the basioceipital. 



Gircumorhitals. — In Amia the circum orbital series is incom- 

 plete above, and the bones are reduced in number ; there is a 

 single praeorbital, two large postorbitals cover the cheek, and 

 above them a smaller one appears at the side of the frontal as a 

 bone of the cranial roof. 



Jaws, Sicspensoinicm,etc.—As already noted, the prsemaxillaries 

 of Aonia have the same relation to the dermal ethmoid, nasals, 

 adnasals and frontals, and to the olfactory sacs and nerves as in 

 Lepidosteus, but the maxillaries are quite unlike those of that 

 genus, for they are unsegmented and free ; each has an inwardly 



Text-figure 7. 



Amia calva. Pterygo-quadrate, suspensorial, and opercular bones. 

 Lettering as in text-fig. 5. 



directed articular process at the anterior end, and each carries a 

 supplemental bone (or supramaxillary). The lower jaw of Amia 

 has two endosteal bones for articidation with the quadrate as in 

 Lepidosteus, but there is an additional small bone in front of the 

 upper of these, and above them is another additional bone with 

 a convex posterior surface for articulation with the concave 

 anterior end of the symplectic. The dentary, angular, and_ supra- 

 angular correspond to those bones in Lepidosteus, and, as in that 

 o-enus. there is a large laminar prajarticular ; in front of this 

 Allis shows two intra-dentaries, but in the skeleton I have 

 examined, the posterior of these is represented on one side by f our 

 bones and on the other by six ; also in my example the endosteal 

 mento-Meckelian figured by Allis appears to be fused with the 

 anterior intra-dentary. 



Proc. ZooL. Soo.— 1923, No. XXX. 30 



