OCR Text |
Show 1904.] OSTEOLOGY OF THE ELOPIDJE AND ALBULID.E. 53 occipital and tlie lower parts of the pro-otics are inflated, just as m Albula, but the subtemporal fossye are larger and shallower. The parasphenoid and entopterygoid teeth are more pointed than those of Aloula; the vomer and palatine are edentulous. The eye-muscle canal has no posterior opening ; the basisphenoid is relatively smaller; the interorbital septum, below the orbito-sphenoid, is membranous; the prefrontal is of slighter construction ; the oval space in the front part of the parasphenoid is very small; the ethmoid region of the cranium is a little shorter in proportion; the top of the mesethmoid has no groove, but the oval foramen seen in a side view of the mesethmoid is present. The shapes, proportions, and relations of the supratemporal and post-temporal are the same as in Albula, although I have not recognised the ossified tendons of the post-temporal projecting into the posterior temporal fossa. The sensory canals of the head, judging by the shapes of the superficial bones, are even relatively larger than in Albula. The circumorbital bones, the premaxilla, maxilla, and surmaxilla do not differ materially from those of Albula. Gunther (I. c.) says " maxillary with a marginal row of very small teeth," but this I cannot confirm. The mandible differs in shape in consequence of the coronoid process being situated farther forward ; it is in the posterior half of the ramus in Albula, but in the anterior half in Bathythrissa. The sesamoid articular of Bathythrissa is unossified. The hyopalatine arch resembles that of Albula, except in the matter of teeth, noted above ; the process of the ectopterygoid which passes outward and backward in the floor of the orbit to join one of the suborbital bones is longer and more slender; the nodule of cartilage which in A Ibula is ossified to form the posterior endosteal palatine is unossified in Bathythrissa, and is connected by a strong ligament with a process of the orbitosplienoid which is directed forward and downward, and lies on the mesial side of the prefrontal. The subopercular is smaller than in Albula, but is of the same general shape; the ventral edge of the interopercular is notched at a little behind the middle of its length. The sensory tube, which runs in the lower edge of the preopercular and beneath the ramus of the mandible, is evidently larger in Bathythrissa than in Albula. There are only six branchiostegal rays, instead of fifteen as in Albula. The first four arise from the outer surface of the ceratohyal, the next from the junction of the ceratohyal and the epihyal, and the last from the outer surface of the epihyal. The only differences to be noted in the hyobranchial skeleton are that the glossohyal has its own teeth, confined to the posterior fourth of its surface, and is not overlapped by the dentigerous membrane-bone that belongs to the three basibranchial bones. The basibranchial teeth stand higher, and are less hemispherical than in Albula. Comments on the Skull of the El op id ye and Albulida?. In reviewing the characters which are common to the skull of the Elopidae and the Albuli'da?, it is perhaps natural that we should |