458 Proceedings of the Royal Society 
vascular canals anastomosed to form a network. From these canals 
numerous dentine tubes arose. Both the core of the tooth and the 
anastomosing canals with their dentine tubes in the semi-lunar base 
of a comb-plate were examples of vaso-dentine. These plates in the 
basking shark may be regarded as an example of excessively developed 
branchial teeth, a development which is co-related with the small 
size and simple form of the maxillary and mandibular teeth, with the 
n on-predaceous habits of the fish, and with the particular nature of 
the food on which it lives. 
This communication will be printed in extenso in the “Journal 
of Anatomy and Physiology,” April 1880. 
5. Preliminary Report on the Tunicata of the “ Challenger ” 
Expedition. By W. A. Herdman, B.Sc., Baxter Scholar in 
Natural Science in the University of Edinburgh. 
(By permission of the Lords Commissioners of the Treasury .) 
I. Ascidiam. 
Last year the Tunicata collected during the “ Challenger ” Ex- 
pedition were entrusted to me for description by Sir Wyville 
Thomson. 
The entire collection comprises from 150 to 200 species, the 
majority of which are new to science. 
As yet only some of the more abnormal Synascidice and about 
half the Ascidice simplices have been carefully examined. The 
present paper is the preliminary report on the AscmiAmE, the first 
family of the Ascidice simplices. 
The family AsciDiADiE is synonymous with Savigny’s genus 
Phallusia , or Forbes’ Ascidia , and includes those simple ascidians 
which are, as a rule, externally characterised by an eight-lobed 
branchial and a six-lobed atrial aperture, as distinguished from two 
other families — the Cynthiad^, with both apertures four-lobed, and 
the MoLGULiDiE, having the branchial six- and the atrial four-lobed. 
This point, the number of lobes round the apertures, though a 
most important diagnostic, does not hold good for all Ascidiadai 
without exception. Indeed, any one of the characters of the three 
families, if employed singly, will be found, while sufficing in the 
