1906.] ANATOMY OF CENTROPHORUS CALCEUS. 881 



all correctly represented, as my figs. 6 & 16 (Plates LVIII. efe LXI.) 

 show when compared with his. The hyomandibular cartilage is, 

 as shown by Gegenbaur, quite separate from the lower jaw, and 

 is only indirectly attached thereto by a broad ligament (fig. 6). 

 Slender ligaments also attach the hyomandibular to the hind 

 extremity of the upper jaw, and the middle of the upper jaw to 

 the hind 2:)art of the lower jaw (fig. 6). The upper jaw is 

 apparently held in its place solely by means of its ligamentous 

 attachment to the hyomandibulai- cartilage and by the large 

 process above mentioned which was loosely inserted into the 

 cartilaginous roof of the oi'bit. I did not detect any ethmo- 

 palatine ligament. As Gegenbaur states, there are three pre- 

 spiracular cartilages (my fig. 6) situated in the front wall of 

 the large spiracular cleft'"'. In connection with the upper jaw 

 'there are two laloial cartilages (enclosed in the folds of skin at the 

 sides of the mouth shown in fig. 4, PI. LTIII.) and with the 

 lower jaw one, on each side (fis'. 6). A prominent vertical ridge 

 of cartilage is situated in the median line on the dorsal siu-face of 

 the spatulate snout (PI. LX. fig. 15). 



With regai'd to the vei-tebral cohunn of C. ccdceus, my figs. 7 

 & 8 (PI. LYIII.) supply all the information necessary. The 

 vertebrfe. are of the ordinarj^ cyclospondylous type ; the apertures 

 for the exit of the dorsal and venti-al bi'anches of the spinal nerves 

 are respectively situated on the intercalary neural plates and the 

 neural plates proper, and there is in transverse section a small 

 canal situated at tlie base of the neural spine, as in some other 

 tSelachians '\ which contains a band of elastic fibres running the 

 whole length of the body doi-sal to the spinal cord. 



In the anterior dorsal fin, the skeleton of which is rej)resented 

 in fig. 9 (PL LIX.), the lai-ge anterior spine does not reach 

 ventrally to the vertebral column, whereas in the posterior dorsal 

 (PI. LIX. fig. 10) it is firmly grafted on, with a small cartilage 

 situated immediately in front of it and on top of the vertebral 

 column. The dorsal skeleton of the caudal fin consists, as shown 

 (fig. 10), of a row of small inclined cartilaginous rods, two of these 

 somactids abutting on each intei-calary neural plate of the caudal 

 vertebra ; ventrally the hfemal spines are pi'olonged. At the 

 anterior extremity of the ventral caudal fin four cartilages are 

 present distinct from the hfemal spines, and, since the cerato- 

 trichia are in this region attached to these and not directly to 

 the hfemal arches, these four cartilages probably represent a 

 vestige of the anal fin. 



The skeleton of the paired fins is represented in figs. 11 & 12 

 (PL LIX.). The pectoral fin is dibasal and possesses a few 

 fringing cartilages on its posterior border. 



30 See Ridewood for a comparative study of this region of the skull in Selachians : 

 " On the Spiracle and Associated Structures in Elasmobranch Fishes," Anat. 

 Anzeig. Bd. xi. (14) 1895. 



31 " Das Natnrliche System der Elasniohrancliier auf Grundlage des Baues und der 

 Entwicklung ihrer Wirbelsaule." C. Hasse. Jena, 1872. 



