1897.] BCHIDNOCEPHALUS, A HALOSAFROID FISH. 271 



exhibit traces of a longitudinal ridge or angulation. No other 

 scales are preserved. 



The fourth and last specimen in the British Mu-seum (no. 

 P. 2114) is preserved on a slab with remains o£ other fishes. Part 

 o£ its soft tissues are shown in places as a blackened film, but, like 

 the other soecimens, it exhibits no clear indication of scales. The 

 low cranium is observable in broken longitudinal section, while 

 there are imperfect impressions of the characteristic pterygo- 

 quadrate arcade and opercular apparatus. There are also impres- 

 sions of ten ver}'' slender and widely-spaced branchiostegal rays. 

 Immediately behind these occurs the clavicle, but no pectoral fin. 

 The vertebrae are well shown, of the form and character already 

 described. The delicate ribs are very short, apparently not 

 reaching more than halfway to the ventral border ; and there 

 seem to be long and slender intermuscular bones crushed across 

 the neural arches both in the abdominal and caudal regions. One 

 of the pelvic fins exhibits six rays, all except the foremost divided 

 in the distal half ; its support is longer than broad and tapers to a 

 point in front ; it is shown in the impression. Six rays are well pre- 

 served in the dorsal fin, and there may have been one or two more 

 beyond. The first of these rays is simple and a little shorter than 

 the others ; the second is also simple, but slightly longer and with 

 distant articulations ; the third is the longest ray, while this and 

 the other three ai'e once bifurcated distally. The anal fin is 

 imperfect at its free border, and the end of the tail is wanting. 



So far as the characters of Echklnocepliahis are shown by these 

 specimens, the Cretaceous fish only appears to differ from the 

 Eecent Halosaurus in three particulars : no scales are observable 

 in the British Museum fossils except along the sensory canal of 

 the "lateral line"; no pectoral fin is distinguishable; and the 

 number of rays in the dorsal and pelvic fins is less than is usual 

 in the existing genus. The first two of these differences, however, 

 may be due to imperfections in preservation ; and Dr. von der Marck 

 has indeed mentioned ' that some specimens exhibit very delicate 

 scales, covering the whole of the trunk. The third point is 

 comparatively insigniticant. Other differences may still be dis- 

 covered in the characters of the i'acial bones and dentition, which 

 remain unknown ; but, in any case, it will be realized that in all 

 essential features the Halosauroid type of fish is one of great 

 antiquity. 



EXPLANATION OF PLATE XVIII. 



Figs. 1-3. Echidnoccphalus frogcheli, W. von der Marck. — L"pper Cretaceous 

 (Senonian) ; Sendenhorst, Westphalia, br., brauchiostegal rajs ; c.r., 

 cranial roof ; c/., clavicle ; fcp;*., ectopterygoid ; cnjit., entopterygoid ; 

 /., enlarged scales of " lateral line" ; md., mandible ; mpt., metaptery- 

 goid ; op., operculum ; pas., parasphenoid ; pmx., premaxiUa ; qic, 

 quiidrate ; s.aj}; suboperculum. 



[The figures are of the natural size, and the original specimens in 

 the British Museum are numbered respectively P. 2111, P. 4481, 

 P. 5949.] 



1 Paleontographiea, vol. xv. (1868), p. 288; iftiaf. vol. xxii. (1873), p. 62 : 

 and ibid. vol. xxsi. (188.5), p. 260. 



