. The Bashford Dean memorial volume :. Fishes; Sharks; Fishes, Fossil. 426 Bashford Dean Memorial Volume diverticulum is given off anteriorly. This is overlaid by the levator maxillae muscle . . The caecum extends as far forward as the anterior knob of the proximal end of the hyoman- dibular, which projects from the articular depression on the auditory capsule. It is not attached to the hyomandibular, but is separated from it by the hyoidean branch of the seventh nerve, which passes just internal and ventral to it. In all probabihty it is homologous with the more extensive caeca mentioned by R
. The Bashford Dean memorial volume :. Fishes; Sharks; Fishes, Fossil. 426 Bashford Dean Memorial Volume diverticulum is given off anteriorly. This is overlaid by the levator maxillae muscle . . The caecum extends as far forward as the anterior knob of the proximal end of the hyoman- dibular, which projects from the articular depression on the auditory capsule. It is not attached to the hyomandibular, but is separated from it by the hyoidean branch of the seventh nerve, which passes just internal and ventral to it. In all probabihty it is homologous with the more extensive caeca mentioned by Ridewood (1896) which have been described in other selachians by Miiller and Van Bemmelen. In Scyllium, for example, the caecum extends inwards over the hyomandibular and becomes firmly attached to the wall of the auditory capsule, being in some way concerned with the function of hearing. A similar caecum is found in Heptanchus, so that here we have another point in which Chlamydoselachus differs from this member of the Notidanidae. Text'figure 83. Anterolateral wall of the left pseu- dobranchial chamber and peripheral wall of the spiracular canal (x 3) of Chlamydoselachus, represented in one plane. , pseudobranchial filament; , spi- racular canal. Drawn from specimen No. I in the col- lection of the American Museum of Natural History. Along the posteromedial side of the deeper portion of the internal spiracular cavity, close to the hyomandibular, there is a narrow cleft with tumid Hps, about 13 mm. long and 5 mm. deep. This cleft (solidly black in Text-figure 82) is the pseudobranchial chamber. The anterolateral lip is decidedly serrate, the posteromedial Hp is slightly serrate. The pseudobranchial chamber will be further described presently. There is some variation in the manner in which the pseudobranchial chamber com municates with the external spiracular aperture. In specimen No. I, on the left side, a bristle inserted into the pseudobranchial chamber, anywhere along
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