ANATOMY OF HETERODONTUS: ENDOSKELETON 475 
on the right side was imperforate on the left. No suprabasi- 
dorsals are found just anterior to the dorsal rays, and the in- 
terdorsals usually cease at about the ninety-fifth, although they 
may sometimes extend a few segments further back. It is diffi- 
cult to make out the exact perforations in the plates posterior 
to the eightieth vertebra, for they may cut the edges of the 
plate and hence the nerve may emerge between the plates. 
4. The anal fin. The base of the anal fin in the specimen 
before me abuts against the fifty-eighth centrum of the spinal 
column. ° But this position varies between the fifty-eighth and 
sixty-third vertebrae. From the basal piece, which is remarkably 
like that of the dorsals, proceed four rows of radials, the first 
composed of two segments; the second has two rows arising from 
it, in the first of which are five cartilages, in the second four; 
the third radial is elongate and is continued by three successively 
shorter pieces; and the fourth, more elongate still, is followed 
by a broader radial. Upon this are three rounded pieces, over 
the first and a part of the:second of which is a broader cap. 
Berkeley, California 
March, 1915 
LITERATURE CITED 
Batrour, F. M. 1881 On the development of the skeleton of the paired fins 
of Elasmobranchii, considered in relation to its bearings on the nature 
of the limbs of the Vertebrata. Proc. Zool. Soc. London. 
FURBRINGER, Kart 1903 Beitrage zur Kenntnis des Visceralskelets der Sel- 
achier. Morph. Jahrb., Bd. 31. 
FURBRINGER, Max 1897 Ueber die Spino-occipitalen Nerven der Selachier 
und Holocephalen und ihre vergleichende Morphologie. Festschrift 
fiir Gegenbaur, III. 
Gapow, Hans 1888 On the modifications of the first and second visceral 
arches, with especial reference to the homologies of the auditory 
ossicles. Phil. Trans. Roy. Soc., B, vol. 179. 
GEGENBAUR, C. 1865 Untersuchungen zur vergleichenden Anatomie der Wir- 
belthiere. II. Brustflossen der Fische. 
1867 Ueber die Entwickelung der Wirbelsiule des Lepidosteus, mit 
vergleichend-anatomischen Bemerkungen. Jena. Zeitsch., Bd. 3. 
1872 Untersuchungen zur vergleichenden Anatomie der Wirbelthiere. 
III. Das Kopfskelet der Selachier, ein Beitrag zur Erkenntniss der 
Genese des Kopfskeletes der Wirbelthiere. Leipzig. 
