76 General Notes. [January, 
THE BATRACHIAN INTERCENTRUM.—The determination of the 
homologies of the segments of the vertebral centra of the rhachi- 
tomous and embolomerous batrachians is a question of impor- 
tance in the history of the evolution of the three classes of land 
Vertebrata, the Batrachia, the Reptilia and the Mammalia. I 
the European paleontologists, especially by Fritsch in his Fauna 
der Gaskohle der Permformation Bcehmens. I have reéxamined 
this question, and with the aid of new material I am able to reach 
further definite conclusions in the matter. 
he facts which I have discovered are the following : 
I. In the Pelycosauria the chevron bones form a continuum 
with the intercentrum! (hypocentrum Gaudry). 
itt caudal vertebrz of Eryops also (Rhachitomi), the 
chevron bones form a continuum with the intercentrum. 
therefore believe the intercentra of Clepsydrops and of Eryops 
to be homologous parts. 
ITI. In the caudal series of Cricotus? (Embolomeri) the inter- 
centra are as large as the centra, and except that they form a con- 
tinuum with the chevron bones, resemble them, and take part 
with them in supporting the neural arch. 
IV. In the dorsal region of Cricotus the neural arch loses its 
articulation with the intercentrum and stands exclusively on the 
centrum.* The serial homologies of the centra and intercentra 
are readily traceable in this genus throughout the column. 
In spite of these facts Dr. Fritsch and others regard the inter- 
centrum of the Rhachitomi (hypocentrum of Gaudry) as the true 
centrum. His reasons for this course are the following: 
I, In the caudal region of Sparagmites and Diplovertebron the 
neural arch stands on the intercentrum,’ so that it is easily mis- 
taken for a centrum. 
II. In the dorsal region in Chelydosaurus and Sphenosaurus, 
the neural arch stands above or on the intercentrum, while the 
centrum (pleurocentrum and hypocentrum pleurale) is reduced in 
dimensions. 
III. It thus results that the small hypocentrum pleurale resem- 
bles the intercentrum of the Reptilia and certain Mammalia, 
rather than the centrum, to which it truly belongs. 
I am of the opinion that the homological determinations of 
Gaudry and Fritsch, in this matter, are erroneous, and for the fol- 
lowing reasons: 
I. The neural arch being free may change its articulation from 
1 Proceedings Amer. Philosoph. Soc., 1878, p. 510. 
2 Loc. cit., 1880. Pal. Bulletin, No. 32, p. 1 5, Pl. nt. fig. §. 
3 Loc. cit., 1878, p. 522. 
*Loc. cit., 1878 522, and 1884, p. 29. Dr. Fritsch has overlooked these refer- 
ences, and wrongly believes that the complete intercentra of Cricotus are confined. 
to the caudal region. 
5 Fauna der Gaskohle, Bd. 11, Heft 1, Pl. 50, fig. 14, 1 5-16. 
