1904. J OSTEOLCKJY OF THE EhOVlDM AND ALBULID.E. 41 



low down, Mud fai- in advance of the endosteal ai-ticulai-, i. e. not 

 as in Albula. The articular facet for the head of the quadrate is 

 formed in its upper j)art by the endosteal articulai-. and in its 

 lower part by the angular- bone, which is fused with the ectosteal 

 articular. 



Hyo'palathie Series (text-fig. 10, p. 40). — The hyomandibulai- 

 ai'ticulates with the cranium by two heads, the anterior one being- 

 smaller and standing out more distinctly than the othei-. Thie 

 palatine articulates with the ethmoid i-egion b)^ a single head, so 

 far as can be seen in the dried skull. The sympleetic makes with 

 the lower limb of the hyomandibular an angle of 1 15 oi' 1 20 degrees. 

 Minute teeth occui- on the palatal surfaces of the palatine, ento- 

 pterygoid, and ectopterygoid Ijones. 



Opercular Series (text-figs. 9 & 10, p. 40). — The shape, size, and 

 relations of the opei-cular bones are so clearly shown in the figures 

 that no description is necessary. The branchiostegal I'ays are 35 

 in number in one specimen, which may be called " specimen A." 

 The first one is attached just beneath the anterior end of the 

 ceratohyal * ; those that follow form a closely-set series along its 

 ventral border, wliile the last fourteen are afiixed to the outer 

 face of the epihyal, and gradually become largei' and flatter as one 

 traces the series backwai-ds. The last three extend farther f orwai-d 

 over the outer face of the epihyal than the others, which has the 

 effect of making the transition to the subopercular and opercular 

 bones a very gradual one. In no modem form is it more cleai'ly 

 seen than in Elops that the opei'cular and subopercular are the 

 two terminal elements of the bi-anchiostegal series. In a largei- 

 specimen (B) the numbers ai-e less — 20 on the ceratohyal and 1 2 

 on the epihyal. In si3ecimen C there are 29 rays on the right 

 side and 31 on the left; in I) there are 28 on each side: but in 

 each of these specimens there are probably some rays missing. A 

 median jugular plate is present, attached by ligament to the back 

 of the mandibular symphysis (text-fig. 10, j/, p. 40). 



Hyobranchicd Series (text-fig. 11, p. 42). — The interhyal is 

 ossified. The epihyal is i-elativelj" large. The iipper and lower 

 hypohyals are approximately equal in size. The glossohyal is a 

 flat cartilage, horizontally disposed, with a minute endosteal nodule 

 in its posterior end, and bearing on its uppei- sui-face a finely 

 dentigerous membrane-bone. The urohyal is long, and extends 

 back as far as the anterior extremity of the fifth ceratobi-anchial. 



A long, finely dentigerous bone ovei-lies the thi-ee basibranchials. 

 The third basibranchial has degenerated in the antei-ior five-sixths 

 of its length into a fatty mass, but the hinder one-sixth is a small, 

 fairly compact bone partiallj' covered by the long dentigerous 

 bone just mentioned, the rest of its uppei- surface being covered 

 by small, uncoalesced, readil^v removable dentigerous plates. The 

 cartilage-plate representing the undifierentiated fourth and fifth 



* The occurrence of branchiostegal rajs along the whole length of the ceratohyal, 

 up to its anterior extremitj^ is to he regarded as a primitive feature, e\en more 

 primitive than the greatness of the number of the rays. Amia is more specialised 

 than Elops in this respect. 



