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. 



p.f., pseudobranchial filament; s.c, 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 its length, passes 

 posteromedially through a sHt-like aperture into the spiracular canal {s.c. in Text-figures 

 82 and 83) which is compressed between the hyomandibular and the integument. The 

 spiracular canal becomes narrower as it approaches the external spiracular aperture. On 

 the right side, the pseudobranchial chamber communicates with the narrow spiracular 

 canal only by way of a small round opening situated at the posterolateral end of the 

 pseudobranchial chamber. In specimen No. II, on the left side, the external spiracular 

 aperture is exceptionally large and leads directly into the pseudobranchial chamber. 

 On the right side, the spiracular canal is hke that on the left side of No. I. In specimen 

 No. Ill, which has unusually small external spiracular apertures, each pseudobranchial 

 chamber opens into the slender spiracular canal by means of a very small aperture situated 

 as it is on the right side of No. I. Thus I find, in my specimens, decided differences in 

 the size of the spiracular canal in the region where it communicates with the pseudo- 



