A. Smith Woodward—On the Genus Synechodus. 499 
No. 49032). All the vertebre are distinctly “‘asterospondylic” in 
structure, and the centra are mostly deeper than long. 
Appendicular Skeleton.—Kach half of the pectoral arch consists 
of a single slender cartilage, produced upwards into an attenuated 
extremity, and very similar in form to the corresponding element 
both of Palgospinaz and of Hybodus. 
External Dermal Structures.—A fine, apparently sparse shagreen 
covered at least certain portions of the body; and a few of the 
granules are well preserved upon one small fragmentary head in the 
British Museum. Some granules are smooth and quadrate in form, 
but many are more or less oval, ridged and grooved in the direction 
of their long axis. 
Affinities—The dentition of Synechodus, as long ago recognized, 
indicates the systematic position of the fish to be in the Hybodont 
section of the great family of Cestraciontide. Many of the detached 
teeth cannot be distinguished from those of Hybodus; but, as already 
remarked, a comparison of the complete dentition described above 
with the dentition of Palzospinax priscus from the Lower Lias of 
Lyme Regis,' shows a still more exact correspondence in almost 
every feature. With Palgospinax, also, Synechodus agrees in the 
character of its shagreen; and the vertebre in the Cretaceous 
genus only differ from those of the Liassic fish in their slightly 
higher stage of development. The fact that no Selachian dorsal fin- 
spines have hitherto been found in the Chalk, except small smooth 
spines indistinguishable from those of Cestracion and Palgospinaz, 
is also suggestive of the correspondence of the two genera under 
comparison in the nature of these dermal defences. The more 
specialized character of Synechodus, indeed, is the only justification 
at present for its generic separation; and it may be added that 
Palgospinax is certainly one of the Cestraciontide (Hybodontide), 
being definitely separated from the Spinacide, with which it has 
hitherto been associated, by the possession of a distinct anal fin 
(Brit. Mus. no. P. 1296). 
Distribution.—The earliest evidence of Synechodus with which the 
writer is acquainted occurs in the Neocomian of Kent, whence have 
been obtained some anterior teeth with an attenuated principal 
coronal cusp. Other teeth have been described from the Lower 
Cretaceous of Amuri Bluff, New Zealand, under the name of Odon- 
taspis sulcata.2, A few teeth, of still another specific type, are met 
with in the English Gault. A single example from the Cambridge 
Greensand is preserved in the collection of Thomas Jesson, Hsq., 
of Northampton. 8S. dubrisiensis occurs in the Lower, and probably 
also in the Upper Chalk; there is evidence of other forms in the 
uppermost Chalk of Norfolk; and one or more species are repre- 
sented in the Lower Chalk of Saxony, Bohemia, and Russia. 
1 Sir Philip Egerton, ‘‘ Figs. and Descrips. Brit. Organic Remains” (Mem. Geol. 
Surv.), dec. xii. (1872), pl. vu. 
2 J. W. Davis, ‘On the Fossil Fish Remains of the Tertiary and Cretaceo- 
Tertiary Formations of New Zealand,” Trans. Roy. Dublin Soe. [2] vol. iv. (1888), 
p. 25, pl. v. figs. 11—13. 
