250 Dr. J. D. F. Gilchrist on the 



striking features, ami may bo consiilered first. The species 

 o£ Psenes, which was found in rather deep water off the 

 coast of Natal, seems to be new, and may be provisionally 

 called P. natuletisis for convenience. 



Psenes natalensis. 



The oesophageal pouches are conspicuous structures lying in 

 the anterior end of the ccelom, apparently on the cesophaous, 

 just behind the pharyngeal region. In a mature sj)ecimeM of 

 150 mm. they measure 16 mm. in length, or slightly larger 

 than the diameter of the eye of the fish. They measure 7 mm. 

 in vertical diameter. Unlike other cases, to be noted later, 

 they lie parallel with the alimentary tract, and do not extend 

 below the level of its lower margin. Externally the whole 

 structure consists of a great thickening of the muscular layers 

 of the splanchnopleure. Internally it is lined by the endo- 

 derra, which expands out on each side dorso-laterally to form 

 the pouches in which the " teeth ^' are lodged. It is the 

 nature of this eudoderm and its tooth-like structures which is 

 in question, but the relation of this wliole structure to the 

 branchial system may first be considered. It is in direct and 

 intimate connection with the fifth branchial arch, the cerato- 

 branchials of which are long and slender. They meet each 

 other ventrally at a point, where they are supported at the 

 end of the basal elements of the other arches. There is a 

 small slit separating the fourth and fifth arch, and on the 

 latter there are about seven reduced gill-rakers. They pass 

 uj)wards on each side of the anterior end of the oesophageal 

 sacs, which they thus support. They are continued dorsal ly, 

 as small epibranchial elements, directed forwards to veiy 

 large well-calcified pharyngo-branchials, which are fused 

 together to form a stout concave structure, in w^liich the mass 

 is firmly secured. The teeth on these upper ])haryngeal8 are 

 well developed, and ibini rounded patches, which lie in the 

 anterior end ot the oesophageal sacs, but do not penetrate 

 further back, nor assume a lobed projecting form, as they do 

 in types noted below. Posterior to these teeth and in the sacs 

 lie the oesophageal teeth. 



The sacs have thick walls, in which two muscular lay(rs 

 may be distinguished — an outer tiansverse layer and an inner 

 longitudinal layer. On removing these, a somewhat remark- 

 able appearance is presented, the whole of the exposed 

 surface being covered with a series of what appears to be 

 overlapping scales, each n)easuring between 2 and 3 mm. in 

 diameter. On removing one of these it was found that 



I 



