52 The American Geologist. J"^^'- i^*^*- 
spine is provided, naturally perhaps, on account of its more 
recent appearance, with more highly differentiated denticles, 
Cf. Fig. iC. The lateral head spine of myriacanthid has hith- 
erto been regarded as a "dermal plate"* and its projecting den- 
ticles have not been perfectly preserved. The writer is, ac- 
cordingly, greatly indebted to professor E. T. Newton of the 
Palseontological Museum in Jermyn street, for the privilege 
of examining an unfigured specimen of "Prognafhodiis gun- 
theri" (Myriacanthus paradoxus), from the classic locality at 
Lyme Regis, which shows these antero-lateral spines in ap- 
proximately their natural position. One observes in passing 
that the spines in this specimen had a well marked basal re- 
gion ensuring their firm attachment, and we have thus addi- 
tional evidence for regarding the group of trachyacanthids as 
an artificial one, Jaekel having maintained that the lateral head 
spines of Menaspis, which are closely to be compared with the 
present spine of myriacanthids are practically without basal 
expansion. 
(2) Dentition. The dental plates, as above noted, are 
four in number, and agree essentially with those of Rhyncho- 
dus. One notes, in this regard, the peculiar ridge passing 
along the buccal face of the plate, which finds its apparent 
homologue in many chimaeroids. How closely its tritoral 
elements correspond remains to be determined by histological 
stud}'- Moreover, as here denoted, the plates agree with those 
of chimseroids in their proportion to the size of the head. , 
(3) Dermal scutes. — These agree in essential characters 
with those of Mesozoic chimaeroids, notably Squaloraja. 
(4) Relations of the mucous canals. — These are denoted 
in the restoration and will be found to agree essentially with 
those of chimsroid. {Cf. Fig. iB.) They are. moreover, 
open canals as in recent chimaeroids. 
(5) Characters of the paired fins. — The basal elements 
resemble strikingly those of Squaloraja. 
(6) ' Disposition of the so-called paired head spines de- 
noted by I, n and III in the restoration, Fig. lA. — These 
structures, shown by Reis to be frbro-cartiFage rather than 
vaso-dentine, apparently correspond to the so-called lip cartil- 
ages of Squaloraja. They are, it is true, unjointed, but from 
♦Both Woodward and Jaekel have indicated that these spines may have 
had their position ou tlie sides of tlie head, Oracantliiis-lil;e. 
