302 PBOF. T. W. BRIDGE ON THE [Apr. 2, 



I also wish to observe on this occasion that the Percopsidae, 

 which are not included in Cope's synopsis and are placed in 

 " Suborder uncertain " by Gill, are most nearly allied to the 

 Salmonidse. As in Salmo, the supraoccipital completely separates 

 the parietals. Prof. Stewart, who has kindly examined bones of 

 Percopsis gutfatus and Oolumhia transmontana at my request, 

 informs me that he has been unable to find a trace of lacunae, 

 although these are present in the bones of Salmo, Coregonus, 

 Thymallus, Stenodus, Microstoma, and Ari/entina ; he, however, 

 finds them likewise absent in Osmerus, Hypomesus, Eetropinna, 

 Sala)ix, and Plccoglossus. 



3. On certain Features in the Skull of Osteoglossum 

 formosum. By Prof. T. W. Bridge, M.A.' 



[Eeceiyed March 28, 189.5.] 

 (Plate XXII.) 



While recently examining a skeleton of a specimen of Osteoglossum 

 formosum, Miill. et Schl., in the Zoological Museum of Mason 

 College, I noticed one or two interesting featm-es in connection 

 with the skuU which, so far as I have been able to discover, have not 

 previously been described. The only reference to the skull with 

 which I am acquainted is by Hyrtl in his " Beitrag zur Anatomie 

 von Heterotis ehrenbergii, C.V." (Denksclir. d. Akad. Wiss. Wien, 

 Bd. viii. 1854, pp. 73-88). In this paper the author briefly 

 compares the skeleton of Osteoglossum with that of Heterotis ; but 

 although the comparison extends to certain features in the 

 structure of the skull in the two genera, Hyrtl makes no refer- 

 ence whatever to those structm-al modifications in the skull of 

 Osteoglossum to which I desire to direct attention. 



On examining the base of the skull of Osteoglossum formosum 

 the parasphenoid (PI. XXII. figs. ] and 2, jis.) is seen occupying 

 its normal position, firmly attached to the ventral surface of the 

 basioccipital behind, and, from that point, extending forwards 

 beneath the cartilaginous interorbital region to its junction with 

 the dentigerous vomers anteriorly. As the parasphenoid passes 

 between and beneath the two prootic bones it forms the floor of 

 a median canal for the muscles of the eyeball, the roof of which is, 

 as usual, formed by the mesial union of the two prootics in the 

 floor of the cranial cavity. At this point the parasphenoid gives 

 off from its lateral margins two well-marked processes on each 

 side : first, an ascending process (ps.l.) which passes obliquely 

 upwards, in contact with the anterior margin of the prootic of 

 its side, and finally terminates above by overlapping the outer 

 surfaces of the prootic (pr.o.), the sphenotic {sp.o.), and the 



* Communicated by Dr. Gunther, F.R.S. 



