The Anatomy of Chlamydoselachus 



359 



presents a striking picture of gradation between jaws and gill-arches. A more nearly 

 perfect gradation is exhibited in Dean's reconstruction of Cladoselache fyleri, shown 

 in my Text'figure 25. Since the ceratohyoids, as well as the hyomandibulars, of 

 Chlamydoselachus bear branchial rays (my Figure 5, plate II), the hyoid arch can scarcely 

 be derived from the velum of an amphioxid ancestor as alleged by Ayers (1931). In 

 Heptanchus (Daniel, 1934) the hyoid segment possesses an extravisceral cartilage, not 

 present in Chlamydoselachus. 



All the branchial arches of Chlamydoselachus, except' 

 ing the sixth and the vestigial seventh, bear branchial rays 

 (Text-figure 77; and Figure 8, plate III). These are very 

 slender rods of cartilage, attached at one end to a branchial 

 arch, and supporting the gill-septum. Goodey (1910.1) 

 states that in his two specimens, male and female respective- 

 ly, the greatest number of rays occurs on the hyoid arch, 

 and as one proceeds posteriorly the number gradually de- 

 creases. His tables showing the number of rays on the 

 right and left sides of each arch, from the hyoid to the fifth 

 branchial arch inclusive, support his statement. The same 

 trend is shown in Collett's (1897) table showing the num- 

 ber of rays for each branchial arch (one side only?), from 

 the first to the sixth inclusive, in his large specimen; but 

 it is probable that Collett's first arch, bearing nineteen 

 rays, is really the hyoid arch, and his sixth branchial arch, 

 bearing eight rays, is really the fifth. 



In each of the first five branchial arches of Chlamy- 

 doselachus there is a dorsal extrabranchial cartilage, de- 

 scribed by Fiirbringer (1903) and by Allis (1923, Fig. 49. 

 pi. XVIII). In Furbrmger's Figs. 31, 32, 33, Taf. XVIII, the 

 extrabranchial cartilages appear like detached or fragmented 

 branchial rays, usually small. 



The basibranchials and hypobranchials constitute the most variable part of the 

 visceral skeleton of Chlamydoselachus. Viewed as departures from an easily recognized 

 type, these variations are interesting. In none of the specimens of Chlamydoselachus 

 that have been described is there a distinct basibranchial associated with the first pair 

 of ceratobranchials. To be sure, Garman (1885.2, p. 11) enumerates a first basibranchial 

 in his series, but this would be a second if the series were complete. In order to make 

 comparisons, one must revise his enumeration to correspond with that used by Goodey 

 (1910.1) and others. With this change of labels, Garman describes and figures separate 

 second and third basibranchials (my Text-figure 24). The fourth basibranchial is fused 

 with the corresponding hypobranchials, is obHquely and indistinctly divided, and is closely 

 joined with the fifth which is fused with the sixth and indistinguishable from it save by 



Text-figure 25. 

 Reconstruction of the underside 

 of the skull of a Devonian shark, 

 Cladoselache fyleri, showing low- 

 er jaw in series with gill-arches. 

 After Dean, 1909, Fig. 6. 



