TRAXSACTIONS OF SECTION D, 71U 



Laliille has promulg-ated a system based upon modifications of the structure of 

 the pharynx. His arrangement of the fixed ascidians seems to me admirable, but 

 his treatment of the pelagic forms is most unsatisfactory. He follows Herdmau in 

 placing Pyrosoma near Cwlocormm and the Didemnidfe, tliough upon different and 

 purely speculative grounds. 8alpa is divorced from Duliolum through an erroneous 

 interpretation of the ciliated pits on the gill of Salpa. 



The subjoined scheme is based upon anatomical and embryological facts. The 

 pelagic caducichordate types possess a single row of undivided branchial slits 

 (protostigmata). This condition is recapitulated, as I have elsewhere shown, in 

 the ontogeny of various fixed ascidians, but the protostigmata of the young post- 

 larval form are subsequently subdivided into rows of minute secondary stigmata. 

 The structure of Pyrosoma and its allies is thus more primitive than that of any 

 of the fixed ascidians. 



The two groups, Thaliacea and Ascidiacea, are distinguished in my scheme 

 upon this basis. My subdivision of the Thaliacea explains itself; that of the 

 Ascidiacea I have adopted, with some modifications, from Lahille. 



TUNICATA. 



Perenitichoedata. 



I. Endostylophora. — Pharynx provided with an endostyle. E.g., Oiho- 



pleura, Frltillaria. 

 H. Polystylophora. — Endostyle absent; pharynx provided witli numerous 

 finger-like processes arranged in rows. E.g., Koiculevskia. 



Cadtjcichoedata. 



T. Thaliacea. — Protostigmata undivided ; cloaca posterior. Pelagic. 



i. Myosomata. — Musculature in bands ; pharynx without internal 

 longitudinal bars ; axis of row of protostigmata oblique or trans- 

 verse; lateral atria small. E.g., Doliolum, Salpa, AncJtinia. 

 ii. Pyrosomata. — Musculature diflPuse ; pharynx with internal longi- 

 tudinal bars ; axis of row of protostigmata longitudinal ; lateral 

 atria coextensive with pharynx. E.g., Pyrosoma. 



II. ^-IsciiZ/rtcert!. —Protostigmata subdivided into rows of secondary sti"-mata ; 



cloaca dorsal. Fixed. 

 i. Stolidobranchia. — Pharynx with internal longitudinal bars ; bars 



solid and ribbon-shaped. E.g., Botryllus, Cynthia, Goodsirea. 

 ii. Phlebobranchia, — Pharynx with internal longitudinal bars: bars 



tubular and vascular. E.g., Perophora, Ascidia, Diazona. 

 iii. Aplousobranchia.— Pharynx without internal longitudinal bars ; 



horizontal membranes present. E.g., Clavelina, Distaplia, Ama- 



rcecium, Didemnum. 



12. On the Vrestnce of Skeletal Elements hettveen the Mandibular and 

 Hyoid Arches o/' Hexacanthus and Lsemargus. ByT>v. Philip White. 



13. On the Presence of a Sternum in Hexanchus griseus. 

 By Dr. Philip White, 



M. On the Creodonta. J?i/ Professor W. B. Scott. 



Our knowledge of this remarkable group of extinct flesh eaters has been of 

 slow growth, and only lately has sufficiently perfect material been recovered to 

 give us an accurate insight into the structure and relationships of several of the 

 more important genera. 



The creodonta are almost exclusively Eocene forms, and especially characterise 



