Messrs. Young on new Carboniferous Polyzoa. 333 
to careful investigations, the class of the Bryozoa* is now 
also referred). 
Further, the type of development of the central nervous 
system, the axial cord or {the chorda dorsalis present in many 
species, the relation of the alimentary tube to the branchial 
sac (Amphioxus), are all exceedingly exact, repeatedly con- 
firmed, and extremely important facts, indicating that the class 
Tunicata presents the fundamental form from which has been 
developed the type of the Vertebratat, hitherto standing iso- 
lated in the systems of the animal kingdom. 
The entire absence of remains of Tunicata in all geological 
formations will probably for ever prevent our knowing the 
transition-forms which united the different kinds of Tunicata 
with the lowest Vertebrata (Amphioxus). 
Considering all that has been said, I give Oscar Schmidt’s } 
view, according to which the Tunicata form a special class of 
Protovertebrata, the preference over all other opinions. 
XLIL—On new Carboniferous Polyzoa. By Professor JOHN 
Youne, M.D., and Mr. Jonn Youne, Hunterian Museum, 
University of Glasgow. 
[Plates IX. & IX. bis.] 
In the number of the ‘Annals and Magazine of Natural 
History’ for May 1874 we described the structure of the Poly- 
zoon Which was named Millepora gracilis by Phillips, Cerio- 
pora gracilis (Phillips’s species), Morris’s Catalogue, Vincu- 
laria gracilis by others; and we showed that the structure 
was such as to justify the institution of a new genus. We 
have now examined Ceriopora rhombifera, Phillips, and have 
detected a central axis in it also, this structure being absent 
in C. similis and C. interporosa, Phillips. In the two latter 
species the cells terminate in a mass of cancellated calcareous 
tissue of varying amount, but never forming a columnar, far 
less a tubular axis. We prefer therefore to leave them in 
the genus Certopora, transferring C. rhombifera to our new 
genus Lthabdomeson. After the publication of our former 
* Chiefly on the basis of the remarkable investigations of Nitsche on 
Alcyonella fungosa, Pall. See also Mém. Acad. St. Pétersb. vol. xy. p. 50, 
+ With respect to this, see Hackel, Gen. Morphol. Bd. ii. p. exvi e 
seqg., and p. 415 et seq. 
t Vergl. Anat. 6te Aufl. 1872, p. 248. See also Hackel, Natiirl. 
Schopfungsgesch, 4te Aufl. pp. 466, 467, Taf. 12, 15. 
