568 MR. T. OiOODEY ON TJ1E SKELETAL [Mar. 15, 



IX. Median Fins. 



In regard to these I have not much to say. My observations 

 lead me to confirm the account given by Garman. It must, 

 however, be pointed out that in his figure (PL xiii.) the small 

 distal segments of the trisegmental radials of the anal fin are 

 absent. 



Fiirbringer (7) gives a good figure of the dorsal fin, and on 

 account of this, and also because Garinan's figures of both dorsal 

 and ana] fins are in the main features correct, I have not deemed 

 it advisable to eive a drawing of these structures. 



X. Summary. 



The following are a few of the most important points dealt 

 with in the paper : — 



1. The Membranous Labyrinth is described and figured for 

 the first time, and it has been found to be of the usual selachian 

 type, resembling rather closely that of Hexanchvs griseus. 



2. In the formation of the centra the following points are 

 especially worthy of note : — 



(a) The presence, at the anterior end of the vertebral 



column, of well-developed, calcified cyclospondylic 

 centra. 



(b) Slight constrictions of the notochord in the trunk region, 



best seen in horizontal longitudinal section, not calcined. 

 The lowest stage in the development of centra. 



(c) In the main caudal region, calcified cyclospondylic centra 



of two sizes are present, corresponding with the doubling 

 in the number of arcualia, which here, more than 

 elsewhere in the vertebral column, grow round the 

 notochord and greatly strengthen the centra. 



3. The terminal caudal region is heterospondylic, and not 

 monospondylic as in many other Selachians. 



4. Tbe musculature and skeleton of the mixipterygia are dealt 

 with fully for the first time. In regard to the musculature 

 I have to record the presence of both mtisc. flexor internus and 

 muse, flexor extemus of Huber. In the skeleton I have found the 

 modified radial /3, and only one small intercalary cartilage b.l, 

 not three as recorded by Gunther. 



XI. Literature. 



1. Ayers. — "The Morphology of the Carotids." Bull. Mus. 



Comp. Zool. vol. xvii. No. 5, 1889. 



2. Braus. — " Leber d. Innervation d. paarigen Extremitiiten, 



etc." Jenaische Zeitschr. xxxi., 1898. 



