from Achanarras Quarri/^ Caithness. 



481 



Remarks on (he foregoing Species. 



1. Ih'ptcru.'i J'alfncif'nucsii. — This i.s by far tli(> most com- 

 mon inA\ at Acliaiiarrns, aiitl, so tar as tlie external characters 

 of the species are concerned, the specimens are the most 

 beautiful which I have seen from any locality in Scotland. 

 They occur from (> to 15 inches in len<^th. 



2. Mesacanthns^ sp. — >S|)ecimens of a small Mesacanthus 

 are not uncommon, but hardly in a sufliciently good state of 

 preservation tor accurate identification as to species. In size 

 and the commoidy twisted or contorted condition of the body 

 they resemble M. pusillus, Ag., of the Moray-Firth beds. 



The genus Mesacanthus was instituted by myself in 1888* 

 for those small species previously referred to Acanfhodes {A. 

 pusilhis, Ag., A. Mitchelli, Eg., A. Peachii, Eg.) which, 



Fi- 1. 



Outline of Acanthodes sulcatus, Ag., much reduced. 

 p, pectoral spines ; v, ventral spines ; a, anal ; d, dorsal. 



Fiff. 2. 



^.t.^P-V\ 



Outline of Mesacanthus Mitchelli, Eg., natural size. 

 sp., intermediate spines ; the other letters as in fig. 1. 



though resembling that genus in having one dorsal spine 

 placed posteriorly to the anal, have in addition a pair of 

 minute intermediate spines on the belly between the pectoral 

 and ventral ones. Messrs. Smith Woodward and Sherborn 

 have, however, in their recently-published ' Catalogue of 



* Geol. Mag. dec. iii. vol. v. p. 511. 



