The Anatomy of Chlamydoselachus 351 



THE CRANIUM 



To illustrate various aspects of the cranium and some closely associated parts of the 

 endoskeleton of Chlamydoselachus, I have selected the excellent figures of Allis (1923j 

 for reproduction in my Plates I, II and III. In connection with his very detailed descrip' 

 tion of the skull, Allis has critically reviewed the work of his predecessors, Garman 

 (1885.2) and Goodey (1910.1). Of the work of Deinega (1909), Allis was probably un- 

 aware since he makes no reference to it. 



Garman (1885.2, p. 8) writes thus of the "skull" (cranium) of his 1510'mm. specimen 

 of Chlamydoselachus: 



The skull of the frilled shark is suggestive of immaturity; the thin walls, soft cartilage, 

 and large pores and foramina with thin edges around them, seem to be those of a young, 

 rather than an adult specimen. Compared with that of Heptabranchias [Heptanchus] 

 it agrees better with an embryo than an adult. Looking at it from above, its shape may be 

 likened to that of the body of a guitar, the vertebral column answering to the neck of the 

 instrument, and the narrow section between the orbits to the middle of its box . . . The 

 walls are very thin. In longitudinal section the thickness of floor and roof is comparatively 

 uniform. There is a marked contrast in this respect if compared with the skulls of Hex' 

 anchus and Heptahranchias, which in these portions are thick and irregular (see Gegenbaur, 

 1872, Das Kopfskelett der Selachier, Figs. 1 and 2, pi. IV) . . . The chamber is large, and the 

 brain small. 



Allis (1923), whose excellent figures showing dorsal, ventral and lateral aspects of 

 the "neurocranium" of Chlamydoselachus are reproduced as my Plate I, says: "In dorsal 

 view [my Figure 1] it greatly resembles the neurocranium of Hexanchus (Gegenbaur, 

 1872), but its dorsal surface is even flatter." Also, in dorsal view the cranium of Chlamy 

 doselachus is much like that of Heptanchus (Daniel, 1934, Figs. 45 and 46). According 

 to Allis the cranium of Chlamydoselachus differs from those of Hexanchus and Hep- 

 tanchus, and resembles those of Acanthias, Centrophorus and Scymnus (Gegenbaur, 

 1872, p. 39) in that the ventral surfaces (Figure 2, plate I) of the occipital and labyrin- 

 thine regions lie in the same level, and in that the eminence of the bulla acustica is found 

 on this ventral surface and not on the lateral surface (Figure 3, plate I) of the neurocranium. 

 This ventral position was considered by Gegenbaur to be secondary, due largely to 

 a greater development of the hyomandibular articular facet than is found in Hexanchus 

 and Heptanchus, or indeed in any other selachian skull figured by him. 



All who have studied the matter agree that the notochord of Chlamydoselachus is 

 continued as a slender strand of tissue in the base of the cranium as far forward as the 

 pituitary fossa. This is clearly shown in Garman's (1885.2) Fig. B, nc, pi. VII; also in 

 my Text'figures 21 and 22 after Ayers, and in my Text-figure 30, p. 364, after Goodey. 

 It is faintly indicated in Deinega's (1909 and 1924) Fig. 4, pi. II; in Goodey's (1910.1) 

 Fig. 2, pi. XLII; and in my Figure 4, plate II (after Allis). This persistence of the anteri- 

 or portion of the notochord in the region of the basis cranii is a very primitive character. 

 To be sure, in all vertebrate embryos the notochord extends forward almost to the 



