100 
DAVIS : NOTE ON CHLAMYDOSELACHUS. 
appears as a new element in Selacliolog-y, and becomes the represen- 
tative of a hitherto unknown type, and throws light on the ancestrj^ 
of some of the extinct forms of the class. He suggests the name 
Pternodonta as preferable to the one given by Mr. Garman, and 
considers the fish to be the type of at least a sub-order. Prof. Gill 
is disposed to consider Chlamydoselachus to stand " nearer the true 
fishes than do the sharks proper, not because it appears to be in 
the line of descent between the two, but because it is nearer the 
primitive line fiom which both types have diverged." Thus far he 
agrees with Mr. Garman, but he dissents emphatically from him in 
regarding the recent acquisition as a Cladodont shark, basing his 
objection mainly on the description by Dr. Traquair of Ctenacanthus 
costeUatus (Geological Magazine, dec. 3, Vol. I., pp. 3-8, pi. 2). 
He agrees with Prof. Cope that Chlamydoselachus did have a 
representative in the Carboniferous genus Diplodus, iVgass (or 
Didj'modus, Cope), although he does not think that the two can be 
congeneric. 
Professor Gill classifies the genera Hybodus, Cladodus, Ctena- 
canthus, &c., selachians without developed vertebrae, but with a 
persistent notochord, in the Lipospondyli ; and the genera Diplodus 
and Chlamydoselachus, vertebral condition unknown, and with teeth 
having fixed bases, he places in Pternodonta or Selachophichthyoidi, 
and ventures an opinion thot the Hybodontid^e may not have been 
Squali at all, but more nearl}^ related to the Holocephali, and that 
both may have diverged from some primitive form theoretically not 
unlike Ctenacanthus. A month later, having seen Professor Cope's 
article in the American Naturalist, Professor Gill entirely changes 
his opinion, and in a communication to Science (Vol. III., No. 62, 
p. 429) he says : " I am convinced, not only that Did^^modus has no 
generic or even family relations with Chlamydoselachus, but that it 
represents even a different order." Then follows a history of Diplodus 
which in consonance with the opinion of the late Sir Philip Egerton 
he places in the genus Pleuracanthus and concludes " as to Chlamy- 
doselachus the anatomy will probably reveal a structure most like 
that of the Opistharthri (Notidanidas) but of a somewhat more 
primitive type." 
