293 Mr. W. Clark on the Chemnitzia opalina a»d C. diaphana. 



upper edge of the operculum being attached to the side of the head 

 by membrane. Posteriorly and above the pectoral the gill-membrane 

 is vertically truncated, and the gill-opening slopes from the level of 

 the upper ray of that fin downwards and forwards till it terminates 

 opposite to the angle of the preoperculum. A row of small scales 

 exists on the suprascapular region, but there are no other scales, 

 nor any bony or spinous points on the head. 



The scales are cycloid and of smaller size than those of Scarus, 

 there being forty-eight in a longitudinal row between the gill-opening 

 and caudal ; seven rows above the lateral line anteriorly, and fourteen 

 below it. 



The scales are oblong, with parallel or converging sides, a truncated 

 or rounded base and a rounded or conical free end. Fine strife, from 

 twelve to twenty in number, diverge from the centre towards the base, 

 but do not produce lobes or crenatures on the margin ; there are some 

 fainter diverging striae anteriorly. The lateral line is arched over the 

 pectoral, and afterwards descends gradually, till opposite the three 

 last dorsal spines, from whence it holds a straight course dovra the 

 middle of the tail and runs out to the middle of the caudal membrane. 

 It is formed of a series of single straight tubes, and is nearly perfectly 

 continuous, especially posteriorly. 



The dorsal spines are slender, and end in soft flexible tips. The 

 first spine stands over the base of the lowest pectoral ray, and is the 

 tallest ; the others gradually diminish in height to the penultimate 

 one, which is a little shorter than the last one ; the soft rays are forked, 

 and rise abruptly to nearly twice the height of the posterior spines. 

 The anal, of similar height and shape to the soft dorsal, has its com- 

 mencement and end a little posterior to those of the latter. The 

 rather small ventrals are attached opposite to the third dorsal spine. 

 The caudal is rather large, and is crescentic at the end with project- 

 ing points, of which the upper one is the longest. 



In general colour the fish appears from Mr. Neill's figure to be 

 blackish-green, deepening nearly to black on the back and dorsal fin. 

 A deep prussian-blue streak covers the second pectoral ray, and there 

 are two broader, interrupted ones on the caudal, viz. between the 

 longest rays of the caudal above and below and the ray immediately 

 interior to them. The iris is likewise blue, and there is a blue spot 

 on the nostrils. These streaks are to be traced on the specimen, but 

 have changed to green. The female differs in being much paler (a 

 dull leek-green in the dried specimen), and in wanting the blue streaks. 

 The lobes of its caudal also are less prolonged. 



XXVII. — On the Chemnitzia opalina and C. diaphana. 

 By William Clark, Esq. 



To the Editors of the Annals of Natural History. 



Gentlemen, Norfolk Crescent, Bath, March 7, 1851. 



I HAVE much gratification in submitting observations on a great 



desideratum amongst malacologists. I have just received in a 



bottle of sea-water, from my friend Mr. Barlee at Falmouth, live 



