^°l89o!"'] PROCEEDINGS OF THE NATIONAL MUSEUM. 379 



Pectorales moderate, with extended procurrent bases, and with all the 

 rays connected by membrane, the lower at least being unbranched. 



Ventrales thoracic, imperfect, being composed each of a spine and 

 three unbranched rays. 



Branchke four, with the slit behind the last arch obsolete. 



Gill rakers short, developed as two rows of dentigerous plates on 

 three arches and one (anterior) row on the fourth. 



Branchial skeleto7i uormal (cottoidean) ; three basibranchials ossi&ed; 

 hypobranchials o£ three pairs in line with the ceraiobranchials of fourth 

 arch suppressed ; ct ratobranchials and epibrancMals of four arches well 

 developed; pharyngohranvMals reduced to one pair of basin-shaped den- 

 tigerous epipharyngeals convex on the dentigerous surface and excavated 

 in the opposite, connected with all the epibranchials j hypopharyngeah 

 divergent and each with a submarginal inferior keel. 



REMARKS. 



Externally the Hemitripterids are distinguishable by a peculiar phys- 

 iognomy and especially by the proportions of the dorsal tin. But the 

 chief differences which are manifested on comparison with other forms 

 are revealed by an examination of the cranium. The principal pecu- 

 liarity lies in the mode in which the floor of the cranial cavity is modi- 

 fied. The myodome is much contracted behind by the depression and 

 appression of the ledge of the basioccipitine to the body of the bone and 

 the parasphenoid and its upheaval only towards its anterior margin; 

 the ledge from the walls of the periotics are tilted very obliquely upwards 

 and connected with each other and the ledge of the basioccipital by 

 broad bands of cartilage ; the basioccipital is also peculiar in being sur- 

 mounted in front of the exoccipitines by partitions nearly parallel but 

 incurved about the middle and sloping outwards, these being connected 

 by cross bars inclosing recesses, one bar being formed by an uptilted 

 shelf of the exoccipital and an anterior one by a thin oblique uplifted 

 shelf; the lateral walls project much beyond these and terminate in 

 trenchant edges.* A character of less importance but still noteworthy 

 is the atrophy or suppression of the median occipital crest, which, -in 

 the Gottid(e, is well developed on the posterior wall of the cranium 

 These differences seem to be supplemented by others of minor impor. 

 tance but whose systematic significance can only be determined when 

 more is known of the osteological details of the numerous genera of 

 Cottidce. 



The scapular arch is typically cottoidean, the upper three enlarged 

 actinosts articulating directly with a cartilaginous extension of the 



"The relations to the soft pars of these structures can only be determined by a 

 careful study of the soft anatomy, for which I have not the material. 



