CHIM^ROIDEI. 57 



any known specimen. Males exhibit a long, slender, prehensile spine (r.), 

 with a broad base, upon the snout ; and there is a cluster of large re- 

 curved denticles on the lower aspect of this spine near its insertion. 

 Conical, radiately-sculptured dermal tubercles are also sparsely arranged 

 both on the head and trunk ; but none are fused into plates. The cranium 

 i-xliibits a narrow median rostral cartilage, and a pair of shorter, more 

 slender cartilages extending forwards from the antero-external angles of 

 the olfactory region. Laterally there are also two pairs of very large 

 labial cartilages (I), tapering and sharply bent backwards at their outer 

 extremities. The dentition (A) consists of thin, transversely curved 

 plates, without differentiated tritoral areas, but marked with a series 

 of hard, parallel, longitudinal corrugations. The vomerine plates are, as 

 usual, comparatively small ; the palatines are closely apposed in the 

 median line anteriorly, but divergent posteriorly. The vertebral rings 

 are especially robust, consisting of several well-calcified concentric lamella?. 

 Each pectoral fin exhibits only two basal cartilages with a single series of 

 radials. The pelvic fins of the male are produced into clampers armed 

 with a cluster of booklets. The " lateral line " and the sensory canals of 

 the head are supported by calcified ringlets. Squctloraja is known only 

 from the Lower Lias of Lyme Regis, Dorsetshire, the type species being 

 S. polyspondyla. 



The family of Myriacanthidae. represented by Myriacan- 

 thus, from the English Lias, and Chimceropsis, from the 

 Bavarian Lithographic Stoue (Upper Jurassic), is specially 

 remarkable on account of the presence in the front of the 

 lower jaw of a median, bilaterally-symmetrical tooth, shaped 

 like an incisor. The normal dental plates, though appearing 

 robust, are as thin as those of Squaloraja, and the punctate 

 tritors have not any very definite limits. The rostral spine of 

 the male resembles that of Squaloraja, but the form of the 

 trunk seems to have been less depressed ; and one species of 

 Myriacanthus is known to exhibit in the male a prolonged 

 snout closely similar to that of the modern Callorhynchus. 



Myriacanthus (fig. 45). The body is laterally compressed, and the 

 rostral cartilage is produced, 1 rearing a terminal cutaneous flap. A few 

 symmetrically -arranged, tuberculated dermal plates occur on the head; 

 and males exhibit a long, pointed rostral spine with a broad base, bearing 

 a cluster of large recurved denticles on its lower aspect. The symphysial 

 surface of the pair of mandibular dental plates is narrow, and the oral 

 surface is covered by an extended punctate tritoral area, almost or quite 

 continuous. The mode of attachment of the median presymphysial tooth 

 is unknown. Each palatine is thin and plate-like, triangular or irregularly 



