BY W. H. TWELVETREES AND W. F. PETTERD. 89 



are apt. to escape notice, when once they have been recog- 

 nised they are afterwards easy of detection. The peduncle 

 is very short, and consequently the shell adheri^s to the rock 

 rather closely. The species has not been recorded elsewhere 

 along the northern coast of Tasmania, and this is quite in 

 accordance with what often happens in the distribution of 

 brachiopoda. Owing probably to their sedentary habit, 

 numerous individuals of a species are found confined to a 

 small area, whilft they are absent over the wide distances 

 which separate different colonies of the animals. The Rev. 

 H. D. AtkinsDn, B.A., informs us that he has dredged speci- 

 mens in the south of the island in D'Entrecasteanx Channel, 

 but that he has never met with any on the North-West 

 Coast. 



The shell is sub-circular in form and generally strongly 

 ribbed. In the smooth variety, however, the pedunculated 

 valve is somewhat sub-trigonal. This difference, though 

 slight, is sufficient to enable us to separate a collec- 

 tion of both kinds at a glance into two series without 

 even paying attention to the presence or absence of 

 ribs. We have subjected the shell of both varietit-s to 

 micro sci'pical examination in thin sections, but cannot 

 declare any difl'erence in the pattern or size of the per- 

 forations. The avera,ge diameter of ihe shell canals is -g-^" to 

 yJ-oQ-", and they are mostly ^-i-g-" to y^Q-" apart, measured from 

 centre to centre. Their diameter, where they open oo the 

 external surface, is about -j^-q". We append illustrations of 

 the perforations found in the Tasmanian shells of this genus. 

 The figures being photogi'aphic and not diagrammatic, may 

 be looked upon as trustworthy representations of these 

 singular structures, considered at various times as connected 

 with sensory organs, with respiratory organs, and with pro- 

 cesses of nutrition. After all that has lieen written on the 

 subject, their function is still unsettled. Striicturallr the 

 perforations are (jruss sections of vertical or oolique canals in 

 the shell, which receive caecal prolongations of the mantle of 

 the animal. 



In this species the brachial apparatus does not materially 

 change with age, and we profess ourselves unable to detect 

 any decided variation in the form of the calcareous lamellae 

 of the smooth and ribbed shells. These supports are minute, 

 and the brachial (or oral) appendages are correspondingly 

 small, being comprised altogether in the central nrea of the 

 shell. In shape the oral arms are incurved cirrhated tubes, 

 the cirri of which are about 1/30" long, and from -j^ to xwo" 

 in diameter. The cirri themselves are hollow tubes, with 

 acuminate terminations and a wavy habit. 



Professor E. Deslongchamps in separating Kraussina, 

 Megerlia, Terebratulina, ListUyris, and Platydia from the 



