ENCHODUS. 01 



there are three peculiar, downwardly-directed, processes of bone. The complete 

 dentary consists of an outer and an inner lamina, firmly united at the upper and 

 lower edges, and enclosing a space for the large nieckelian cartilage. The inner 

 lamina is shown in the specimen represented by Agassiz, lor. cit., fig. 4, and is 

 excavated behind. The outer lamina is slightly incurved below and is ornamented 

 on its exposed face with closely-arranged and finely-tuberculated ridges, which 

 radiate backwards from the symphysis. The teeth on the dentary bone are 

 arranged in two rows. On its extreme outer border there is a regular, close series 

 of very small and slender conical teeth, which are nearly uniform in size but 

 slightly largest at the end of the symphysis. These teeth are often wanting in the 

 imperfect fossils, but most of them are indicated in fig. 1, and two or three are 

 preserved at the anterior end of the dentary shown in fig. 7. The inner row com- 

 prises only six to eight widely-spaced, slender, lanceolate teeth, which have 

 sharp anterior and posterior edges and delicately striated faces. Some of them 

 exhibit a slightly sigmoidal anterior edge which imparts to them a gently recurved 

 appearance. The foremost tooth is much the largest, at least twice as long as any 

 of the others; and it is seen with its replacing tooth (,«.) in fig. 7. The second 

 tooth and the hindermost tooth are the smallest of the series. The general aspeet 

 of the jaws is diagrammatically represented in Text-fig. 13, p. 59. 



The preoperculum (figs. 1 , 8, pop.) is deep and narrow, without a lower limb, 

 but tapering to a point above and expanding into a small triangular lamina 

 below. The vertical groove on its outer face for the slime-canal is deep and large ; 

 the ridge of bone in front of this groove is tuberculated ; while the narrow wing 

 behind and below it is ornamented with short radiating ridges which terminate at 

 the posterior and inferior edge in crenulations. The operculum is more than half 

 as wide as deep, and has the peculiarly rounded form indicated in fig. 1, op. Two 

 imperfect examples of this bone are described by Agassiz as scales, loc. cit., p. 65, 

 pi. xxv c, figs. 14, 15. Its external face is ornamented with a close series of 

 finely-tuberculated ridges, which radiate from the rather low point of suspension ; 

 and between some of these ridges there are short intercalated rows of tubercles at 

 the margin of the bone. The inner face of the operculum is strengthened by a 

 small ridge extending horizontally backwards from the point of suspension. The 

 suboperculum (sop.) is partly obscured in fig. 1, but better seen in fig. 8. Its 

 outline is nearly that of an equilateral triangle, and its outer face is ornamented 

 with finely-tuberculated ridges which radiate downwards and backwards from its 

 antero-superior angle. As on the operculum, there are short intercalated ridges 

 or rows of tubercles between the distal ends of the main ridges. The branchio- 

 stegal rays (fig. 1, br.) are wry slender, as especially well shown in 15. M. 

 no. 25921. 



Very few vertebrae of this species are known, hut the abdominal series. 

 followed by three or four anterior caudals, is represented in fig. 1. The centra in 



