492 Bashford Dean Memorial Volume 



missural canal, but it is impossible to state whether the present condition of these canals 

 is vestigial or rudimentary. It is certain, however, that the condition of all the canals, 

 but especially those in this region, is very unstable. Some variations in the hyomandibular 

 region are shown in Text'figure 128c and d; other variations, in the pelvic and caudal 

 portions of the lateral line, are represented in Text-figure 128e. Additional examples of 

 variation in the posterior course of the lateral line are described by Gudger and Smith 

 (1933, pp. 288-9) in three adult specimens. 



Hawkes concludes that the lateral line system of Chlamydoselachus is primitive as 

 regards: (1) the open condition of a portion of the canals; (2) the cutaneous rather than 

 subcutaneous position of the canals; and (3) the entire absence of tubules in many places. 

 In the occipital and hyomandibular region, however, the system tends to a considerable 

 topographical complexity. Again there are indications, in the occipital and lateral canals, 

 of either a vestigial or a rudimentary complexity. 



In Heptanchus (Daniel, 1934), anterior to the spiracle and just posterior to the 

 endolymphatic duct, a small transverse or supratemporal canal passes off from the lateral 

 canal toward the median line. This, however, does not meet and fuse with the similar ca- 

 nal from the opposite side. In Heptanchus maculatus there may be two supratemporal 

 canals on a side, one posterior to the endolymphatic duct, the other anterior to it. Thus 

 we find evidence, in this region, of a variability somewhat comparable to that described 

 in Chlamydoselachus. In Heptanchus, Daniel describes a "gular line" of pit organs corre- 

 sponding in position to Carman's gular division of the sensory canal system in Chlamy 

 doselachus. Allis (1923; 1934), like Garman, describes and figures the gular line as a part 

 of the canal system. ''The spiracular and gular canals [of Chlamydoselachus] form 

 a continuous open groove" (Allis, 1923). This statement holds, without exception, for 

 both right and left sides of my four large specimens. Norris (1929) writes: "The 

 mandibular series of pit organs in Squalus (Norris and Hughes, 1920) and Mustelus 

 (Johnson, 191?) evidently correspond to the gular canal organs in Chlamydoselachus 

 (Hawkes, Allis)". 



Many other comparisons of the sensory canal, ampullary and pit organs of Chlamy- 

 doselachus with those of other elasmobranchs are elaborated in the works of some of the 

 authors cited, but these involve details that cannot be considered here. 



DISCUSSION 



The present section is concerned with the phylogenetic significance of the anatomical 

 characters described on the preceding pages. In every section of this article, comparisons 

 have been made between Chlamydoselachus and other vertebrates, so that it is not neces- 

 sary to enter into details here. 



My own interest in Chlamydoselachus relates chiefly to the evolution of organs and 

 organ systems as such. Nevertheless, while studying this shark I have been impressed 

 by certain things that have a bearing on the question of its phylogenetic affinities : first, 



