428 Bashford Dean Memorial Volume 



In elasmobranchs the spiracle ordinarily differs from the gill'slits in never possessing 

 gill'filaments, though it often has traces of these as a few small folds of the lining of its 

 anterior wall, which constitute the pseudobranch or mandibular gill. AUis (1923, p. 

 169) mentions pseudobranchial filaments in the "'spiracular canal" of Chlamydoselachus, 

 but does not describe them. Goodey (1910.1, p. 550) writes of his specimens of Chlamy- 

 doselachus: "'The pseudobranch in each spiracle consists of about ten short ridges, 

 which lie on the anterior outer wall just inside the external aperture. In the Noti' 

 danidae the pseudobranchs are said to be better developed than in any of the [other] 

 selachians, so that in this respect we find Chlamydoselachus presenting a small difference 

 from Heptanchus and Hexanchus.'" 



In my specimens I have distinguished a special chamber communicating with the 

 internal spiracular cavity (i.s.c.) on the one hand and the spiracular canal (s.c.) on the 

 other, which I call the pseudobranchial chamber (Text-figures 82 and 83). This chamber 

 presents for examination two surfaces, anterolateral and posteromedial respectively. 

 In specimen No. I each surface is about 13 mm. long (measured on the side toward the 

 internal spiracular cavity) and 5 mm. wide (measured from the internal spiracular cavity 

 to the beginning of the spiracular canal). Toward the internal spiracular cavity each 

 of these surfaces is bounded by a distinct ridge or lip, decidedly serrate in the case of the 

 anterolateral lip, only slightly so in the case of the posteromedial lip. The peripheral 

 boundary is not so well defined, save in those cases where the two surfaces meet on the 

 side toward the integument, leaving only a small round aperture leading from the postero- 

 lateral end of the pseudobranchial chamber into the spiracular canal. In cases where 

 the passage into the spiracular canal is large (as shown in Text-figures 82 and 83) the 

 boundary between this chamber and the spiracular canal may be defined as the line where 

 an abrupt change in direction occurs — for the pseudobranchial chamber lies along the 

 anterolateral surface of the hyomandibular, the spiracular canal along its peripheral 

 surface. 



On the anterolateral wall or surface of the pseudobranchial chamber, the pseudo- 

 branchial filaments (Text-figure 83, p.f.) begin at regular intervals along the serrate lip 

 and extend peripherally for a distance varying from 2 to 5 mm. The serrations corre- 

 spond to the filaments — that is, the projections, which appear tooth-like when the lips of 

 the pseudobranchial chamber are approximated, are seen to be the proximal ends of the 

 folds or filaments when the chamber is opened to view. The pseudobranchial filaments 

 are little more than mere ridges; the height of these filaments seldom exceeds 1 mm. 

 and is never more than 1.5 mm. The longest filaments are usually those near the middle 

 of the row. Some of the filaments — particularly those of the left pseudobranchial chamber 

 of specimen No. II, which has the largest filaments — are free at their peripheral ends, 

 where they project as finger-shaped structures as in the case of ordinary gill-filaments. 

 The number of filaments composing each pseudobranch varies from eight to sixteen. 



So far as I know, a pseudobranch on the posteromedial surface of the pseudobranchial 

 chamber has never been described in any elasmobranch. Nevertheless I find, on this 



