4 MYBIACANTHUS PARADOXUS. [Feb. 1906, 



culated dorsal fin-spine. In these three respects it differs from all 

 other known Chimseroids — even from the comparatively-primitive 

 types which have been discovered during recent years in the 

 Japanese seas. 1 The Myriacanthidse, in fact, have still no nearer 

 ally than Callorhynchus, with which Egerton originally compared 

 his so-called u Ischyodus orthorhinus.' 



EXPLANATION OF PLATE I. 



Fig. 1. Myriacanthus paradoxus, Agassiz ; remains of anterior portion of fish, 

 with dorsal fin-spine, one-quarter natural size. — Lower Lias ; Black 

 Ven, Lyme Kegis. [Brit. Mus. no. P. 10130.] d.f, dorsal fin-spine ; 

 l.pa, left palatine dental plate ; md, right mandibular dental plate ; 

 pet, cartilage of pectoral arch; ps, presymphysial tooth; r, rostral 

 cartilage; r.pa, right palatine dental plate; ?, frontal spine or tena- 

 culum ; v. vomerine dental plate ; 1, 11, in. dermal plates. 



2. Presymphysial tooth of the same specimen, inner aspect, natural size. 



3. Dermal hooklets from the rostrum of the same specimen, two being 



of tbe natural size, and the cluster (3" a) enlarged sixteen times. 



4. Dermal plate 1 of tbe same specimen, natural size. 



5. Corresponding dermal plate of another specimen of the same species, 



natural size. [Museum of Practical G-eology, Jermyn Street, no. 1545,1 



1 S. Gartnan, ' Tbe Chimseroids, especially Bhinochimara & its Allies 

 Bull. Mus. Comp. Zool. Harvard, vol. xli, no. 2 (1904), with fifteen plates. 



