16 NORTHERN ZOOLOGY. 



branous flap. The operculum is armed with a spine which scarcely projects through the skin, 

 and also with three smaller points, visible only when the skin dries. The inter operculum and 

 suboperculum are unarmed, and the latter is terminated by the membranous tip of the gill- 

 cover. The supra-scapular is rough with a projecting edge, and the humeral bones have also 

 a prominent edge which is toothed. There are various patches of scales on the top of the 

 head, cheeks, and gill-covers, and the frontal bone exhibits several furrows through the thin 

 integuments. The Branchiostegous membranes overlap each other at their insertion into the 

 isthmus, and contain seven cylindrical curved rays. 



Fins.— Br. 7; D. 15/— 21 or 22; P. 14 or 15; V. 1/5; A. 1/12 ; C. 16 or 18. 



The first dorsal has fifteen spinous rays. The second, commencing an inch behind the 

 termination of the other and over the anus, contains twenty-one or twenty-two rays. The 

 caudal fin is crescentic at its extremity, and is partially scaly towards the base. 



Viscera. 



On laying open the abdomen the liver appears lying transversely on the stomach and cseca : a 

 triangular flap hangs from its centre, but it is not otherwise divided. The bile is pale ; the duct 

 of the gall-bladder opens into one of the caeca The oesophagus is distinguished internally from 

 the stomach by its longitudinal folds : it is short, and before it is slit open appears to be con- 

 tinuous with the first intestine, the stomach looking like a little bag attached to the side of 

 the canal. The lining of the stomach has a light red colour, and being more ample than the 

 exterior coats, is disposed in large crowded and convoluted folds : the pylorus is near the car- 

 diac orifice, the greater part of the stomach being a blind sac. About an inch below the 

 pylorus three caica * open into the intestine, which they equal in calibre. Their structure is 

 similar to that of the intestine, consisting of a peritoneal coat with longitudinal fatty bands, a 

 muscular coat with longitudinal fibres, a firm gelatinous coat, much thicker than the others, 

 and an internal lining disposed in very minute folds. The intestine makes two convolutions, 

 in the second of which its coats become gradually thinner and its calibre less, until it termi- 

 nates in the rectum by a circular projection or valve. The rectum is short, and its diameter 

 is equal to that of the gut near the stomach. The spleen lies in the first duplicature of the 

 intestine. The air-bladder is forked at its upper end, and a small duct, proceeding from its 

 middle, terminates in the same caecum with the gall-duct f . There are a number of red- 

 coloured fatty substances attached to the lining of the air-bladder. 



* L. sandra has four caeca. 



•f This passage stands so in my notes. I acknowledge that my dissections being carried on in cold weather, and in an 

 apartment into which the light was admitted through a small parchment window, I may have mistaken a fold of perito- 

 neum, or a band of vessels, for a duct. But if the duct really terminates in the caecum, it seems to furnish an argument 

 against M. Agassiz's opinion of the air-bladder being an organ of respiration, almost equally strong with that derived from 

 the entire absence of that viscus in many fish. 



