| OCR Text |
Show 4 8 8 DR. W. G. RIDEWOOD ON THE CRANIAL [D e c . 1 3 , continuous with the pair of great cartilages which curve upward from the suturally united posterior ends of the fourth and fifth ceratobranchials. The upper ends of these gieat cartilages meet in the middle line above, but do not fuse ; from the anterior edge of each there stretches forward an extensive tract of thin, but tough membrane, which fills in the angle between the body of the fourth epibranchial and the remarkably long process of the same which slopes upward and backward from near its anterior end. The first three epibranchials are of approximately the same length, but the fourth is longer and wider. The first pharyngo - branchial is a forwardly directed cartilage of conical shape, and there is an upright spicular bone rising from the junction of this with the front of the first epibranchial. There are no teeth on any part of the hyobranchial skeleton. S ummary. On comparing the foregoing accounts of the cranial osteology of Chirocentrus, Clupea, Pellona, Pellonula, Pristigaster, Hyper-lophas, Chatoessus, Dussumieria, Engraulis, Coilia, and Chanos, the most important features of resemblance and difference appear to be as follows. The pai'ietal bones are rather small in size *, and aie separated the one from the other by the supraoccipital. In Coilia, however, they nearly meet in front of the supraoccipital, and in Chanos, owing to the fusion of the commissural sensory-canal bones with the parietal bones, the latter appear to meet over the top of the supraoccipital f. There is a fontanelle between the anterior ends of the two frontal bones in Chirocentrus, Clupea, Pellonula, Pellona (a mere cleft in this genus), and Chatoessus, but not in the other six genera. In Coilia and Engraulis the mesethmoid projects considerably in advance of the vomer, which is not the case in the other genera. Of the genera under consideration, the only one in which the posterior temporal groove is roofed over is Chanos. The temporal foramen appears to be a special feature of the Clupeoid skull. It is an aperture, usually oval in shape, with the long axis horizontal, bounded by the frontal and parietal bones. In 110 instance have I found the postfrontal bone forming part of the boundary, although Boulenger regards this as the normal condition +. The only departure from the general rule that has come within my knowledge is in the case of Engraulis, in which a small portion of the squamosal may come between the parietal and the frontal in the * Small is, of course, but a relative term, and opinions may differ as to the employment of the word. ‘ ‘ Tres petits," the expression used by Boulenger (Poissons du Bassin du Congo, 1901, p. 123), appears to me to convey an exaggerated idea of the smallness of the parietal bones. I leave the figures that illustrate this paper to speak for themselves. f Cope, it is worth noting, included the Lutodirida; (i. e. Chanidae) under the heading " Parietals united " (Trans. Amer. Phil. Soc. n. s.'xiv. 1871, p. 455). X Poiss. Bass. Congo, 1901, p. 123. " Un grand trou de chaque cote du crane borde par le frontal, le postfrontal, et le parietal." |
