354 



University of California Publications in Zoology [Vol. 16 



text-fig. B) back to the fifth are of large size and the fifth is divided 

 into two segments, the upper of which is similar to the sixth hypo- 

 branchial. The seventh or last arch, like the fifth in pentachid forms, 

 has its pharyngobranchial fused to that of the sixth arch. Like 

 pentanchid forms also, the eeratobranchial of this arch is hyper- 

 trophied, but the most interesting departure seen in the seventh arch 



Fig. A. First branchial arch, Ueptanchus maculatus (xl). 



h.r., branchial ray; cb., eeratobranchial cartilage; eh., epibranchial 

 cartilage; ex.h., extrabranehial cartilage; lib., hypobranchial cartilage; pb., 

 pharyngobranchial cartilage. 



is a clearly marked rudimentary hypobranchial (see hV , left side, 

 text-fig. B). To a further discussion of the region we shall return. 

 In the mid-ventral line (text-fig. B) right and left arches are 

 united by basal pieces, or copulae. These pieces in Heptanchus macu- 

 latus differ greatly from those described for Heptanchus cinereus 

 (Gegenbaur, 1872, pi. 18, fig. 1), but they are similar in general plan 

 to those figured by him for He.ranchus. The first of these is the broad 

 basihyal piece (&/».). This cartilage, unlike that described in 

 Chlamydoselachus (Goodey, 1910, pi. 43, fig. 6), is not perforated by 



