54 FOSSIL FISHES OF THE ENGLISH CHALK. 



bone. This element is completely ornamented except along a narrow area 

 anteriorly and antero-superiorly ; and its rows of tubercles radiate from a point 

 opposite tbe spine. The suboperculnm (fig. 8, sop.) is comparatively small and 

 narrow, not curving round the hinder l)order of the operculum. The rows of 

 tubercles forming its external ornament incline downwards and backwards. The 

 interoperculum must have been very small. Nine branchiostegal rays are seen 

 in the original of fig. 1 {br.). 



The greater part of the vertebral column is shown in the type specimen in the 

 Willett Collection, and in a smaller specimen in the British Museum (no. 43388). 

 The total number of vertebras seems to have been about forty-five, and at least 

 tAventy-one of these belong to the caudal region. All the centra are longer than 

 deep and much constricted, with very slight development of a lateral longitudinal 

 ridge. Sections seem to show that they were pierced by a delicate persistent 

 strand of notochord (B. M. no. P. 1703 d). The neural spines are very slender, 

 each fixed to the postero-superior angle of a low neural arch which occupies only 

 the anterior half of the supporting centrum (fig. 1). The ribs are also slender and 

 nearly straight, directly articulating with the middle of each centrum. They are 

 antero-posteriorly compressed, not rounded in section. The neural and haemal 

 spines in the caudal region are rather short and much inclined backwards. 



The pectoral arch is suspended from the cranium by a pair of large laminar post- 

 temporal elements (the left shown in fig. 9), which impinge on the supraoccipital at 

 the middle of the occipital border. They are thin and nearly rhomboidal in shape, 

 about twice as long as broad. The greater part of their outer face is smooth, the 

 ornament of radiating lines of fine tubercles being restricted to a small elongate- 

 ovoid area postero-externally. The supraclavicle is deep and narrow, ornamented 

 at its hinder margin with a few rows of small tubercles, which radiate slightly at 

 the top, but mainly follow its long axis. The clavicle (fig. 1, cl.) consists mainly of 

 a lamina of bone extended in a plane at right angles to the axis of the trunk ; but 

 it also bears a small outer plate in the plane of the flank. In the specimen figured 

 the bone is incomplete below, and its outer plate is smooth ; but the latter must have 

 originally borne a tubercular ornament, which is shown in other specimens {e. g., 

 B. M. no. P. 3657). The post-clavicle is a small, narrow, smooth lamina, which is 

 inclined downwards and l)ack wards from beneath the upper part of the clavicle. 

 The element of both sides is shown in the original of fig. 1 {pel.), and that of the 

 left side is seen in fig. 8 {pel.). The coracoid bears a long and narrow process 

 extending forwards to the symphysis of the clavicles (B. M. no. 39073). The 

 pectoral fin (fig. 1, ptct.) is rather large, long and narrow, consisting of about twelve 

 to fifteen rays, each of whicli has a long unarticulated base ornamented on its front 

 edge with very fine tubercles. As shown by the type specimen, the pelvic fins are 

 nearly as large as the pectorals, each with at least eight rays supported by a nuich- 

 expaiided pelvic bone. 'J'here are traces of these fins and their supj)orts in the 



