1907.] ON THE AXATOMY OF CHLAMYDOSELACHUS. 471 



The following papei'S wei-e read : — 



1. On the Abdominal Viscera and a Vestigial Seventh 

 Branchial Arch in CMamijdoselaclms. By Mrs. 0. A. 

 Merritt Hawkes, M.Sc. (Zoological Laboratory, 

 University of Birmingham).* 



[Received March 23, 1907.] 



(Text-figures 138, 139.) 



Introduction. 



The following notes on the abdominal viscera of Chlam.ydo- 

 selachus angtdneus (Gar.) are published, because the first writer on 

 this species, Garman (1), had only a partly eviscei-ated female, and 

 the second writer, Giinther (2), gave only a general description 

 which does not make note of the distinctive characteristics of 

 Chlamydoselachus. On some points, my specimens did not agree 

 with either that of Garman or those of Giinther. 



As the heart has already been described by both Giinther and 

 Garman, it has not been necessary to make any further reference 

 to that organ. 



In this paper, an attempt has been made to look upon the 

 alimentary viscera from the functional as well as the anatomical 

 point of view, hence suggestions have been made to attempt to 

 explain certain Chlamydoselachian peculiarities. 



Garman has given a description and a figure of the branchial 

 arches, but in his specimen there was obviously no trace of the 

 vestigial seventh arch. It is probable that this arch and its 

 nerve-supply t are of a very variable character, as is frequently 

 the case with vestigial structures. 



The Alimentary Canal. 



The general arrangement of the alimentary canal in Chlaviydo- 

 selachus is, in most of its features, typically Elasmobranchian. 



There are thirteen rows of teeth on each side of the upper and 

 lower jaws, making a total of 52 rows, instead of 51 as stated by 

 Garman (1). The arrangement is, as would be expected, bi- 

 laterally symmetrical. In every specimen examined, however, 

 there was a torsion of the left front row of teeth towards the right 

 side ; and in one case this resulted in a median row of teeth as 

 described by Garman, but the total number of rows of teeth was 

 still 52. 



Garman found six functional teeth in each row, but the 

 specimens examined by me had generally five, although in some 

 cases six. 



* Communicated hy Professor Beidge, F.Z.S. 

 t See Proc. Zool. Soc. 1906, p. 983. 



