SKELETON OF LEPIDOSTKUS. f 5l 



think that there can be little doubt that the hyomandibular 

 is the true epihyal, i. e. the epibranchial of the hyoid ai-ch. 



Vertebral Column. — The vertebrne are solid and opisthocQ3lous, 

 with the neural arches and parapophyses ankylosed to the centni. 

 The vertebrte number 66 ; from tlie fifty-third the vertebral column 

 curves upwards and the vertebra decrease in size. The neura- 

 pophyses of the first two vertebras are short and stout; those 

 of the succeeding vertebrfe are prolonged into slender spines ; the 

 spinas of each pair are in contact distally, but remain separate ; 

 the last six vertebrae have no neural spines and the last three 

 iio distinct neurapophyses. Tlie series of supraneurals extends 

 backwards from the first vertebra to the dorsal fin, and reappears 

 above the end of the vertebral column, where 4 bones (epaxial 

 supports of the caudal fin) are probably to be interpreted as 

 belonging to it. Each supraneural is more or less expanded or 

 even bifid proximally ; the first two are short and stout, and 

 articulate with the neurapophyses of the first two vertebrfe ; the 

 rest are slender, attached to the neural spines. The ribs are 

 expanded proximally for articulation with the distal ends of the 

 strong transverse parapophyses. From the forty-first vertebra 

 backwards the parapophyses become shorter and are directed 

 downwards ; their ribs also are downwardly directed, and behind 

 the anal fin unite to form hfemal spines ; the haemal spines of 

 the upturned vertebrae are expanded as hypurals to support the 

 caudal fin ; the hypurals are only one less in number than 

 the upturned vertebrae, but in the specimen examined they are 

 displaced, so that the sixtieth vertebra bears two and some of 

 the last six vertebrae do not bear any. 



Fin Skeleton. — The dorsal and anal fins are supported by a 

 series of pterygiophores, each of which is divided into a long 

 pi'oximal (basal) and a short distal (radial) segment ; each fin-ray 

 is articulated to its radial. The pelvic bones are rather long and 

 flat ; they converge and slightly overlap anteriorly ; only the 

 innermost radial is well developed, the fin-rays articulating 

 directly with the pelvic bones. The pectoral arch includes a 

 small simple post-temporal, which is firmly united to the skull, a 

 supra-cleithi'um, and a cleithrum. The coracoid cartilage has 

 only one ossification, the hypercoracoid (or "scapula"); there 

 are 4 radials, 3 of which articulate with the hypercoracoid and 

 one with the metapterygium. 



Comparison of Lepidostevs with Am/a. 



Cranium.— In Ainia the orbito-rostral part of the skull is 

 much shorter and broader than in Lejnclosteus, and the cavum 

 cranii extends forward between the orbits to the ethmoid region. 

 On the upper surface a single pair of loose dermo-occipital plates 

 represent the three pairs or more of Le'pidostetts ; the other bones, 

 parietals, pterotics, frontals, proimaxillaries, nasals, adnasals, and 

 dernial ethmoid, have precisely the same relationship to each 



