BRITISH FOSSILS. 



8 



lateral flexure in the organs of locomotion in Nothosomus, while 

 the necessary support was provided for by the fulcral scales and 

 strengthened borders of the anterior rays. The dorso-ventral series 

 contain eight scales, slightly inclined backwards. The mucous 

 duct pierces the third row from below, this being the position of the 

 largest scales ; the row next below it being the next also in size. 

 These and the two rows above the lateral line are considerably 

 larger than those above and below, until near the region of the tail, 

 where all the scales are nearly uniform in size. The scales are thick, 

 compact, and highly lustrous. The outer surface is smooth, and the 

 free margins entire. The inner surface is provided with a broad 

 perpendicular band, occupying the centre of the scales on the flanks, 

 but extending over the entire inner area of the caudal scales. Each 

 band terminates above in a strong pointed process, which locks 

 into a corresponding depression on the lower margin of the scale 

 next above it. Eeceding towards the tail, these processes become 

 gradually more and more obtuse, until they disappear altogether^ 

 and the few most distal scales are united by apposition of the broad 

 margins of the bands. In Pholidophorus and the allied genera the 

 scales covering the centre of the flanks are commonly larger than 

 those on the upper and lower margins of the body ; but there is 

 always a more or less graduated passage from the one form to the 

 other, by the interposition of scales of intermediate dimensions, 

 even in Pholidophorus pachysomus, where the extremes are most 

 exaggerated. The details above given show that in Nothosomus, 

 the flanks are protected by four rows of large scutiform scales, suc- 

 ceeded above and below by small scales, the transition from the 

 one form to the other being abrupt. In this respect Nothosomiis 

 has some resemblance to the sauroid genera Aspidorhynchus and 

 BelonostomuSj but in all other respects it appears to be a legitimate 

 member of the Lepidoid family. 



Locality, — The Lias of Street, Gloucestershire. 



Explanation of Plate. 



rig. 1. Nothosomus octostychius, size of nature. 



Fig. 2. Dorsal fin, magnified. 



Pig. 3. Ventral fin, magnified. 



Fig. 4. Anal fin, magnified . 



Fig. 5. Caudal fin, magnified. 



Fig. 6. Tail of Pholidophorus, magnified. 



P. DE M. Grey Egerton. 



February 1857. 



