146 ME. E. DAT ON THE SPECIFIC IDENTITY 



growth and attrition of the Walrus-tusks. He observes that 

 growth does not necessarily proceed pari passu with attrition, and 

 consequently tusks of the same age may be of various lengths ; 

 the "biggest tusks, cceteris paribus, will be those which have suffered 

 least rubbing during the process of growth. The causes of attri- 

 tion are not merely due to friction of the points upon ice studded 

 with sand particles, but rather to the digging up of the sea- 

 bottom when the Walrus is in search of mollusca, or when scraping 

 rock-surfaces to detach limpets and such like. As regards the 

 sea-bottom and shore, it is hardly possible to doubt that the 

 Miocene (Diestien) sea, with its Pyrula, Voluta, Cassidaria, JPho- 

 ladomya, and such forms, and its Teuthophagous whales {Zipld- 

 oids) and its huge sharks, was not an ice-bound sea. The Walrus' 

 tusks, then, are only secondarily, and not primarily, related to its 

 movements upon shore-ice. With no very hard rocks against 

 which to wear down its tusks, the Diestien Walrus accordingly 

 had them longer, of greater primitive curvature, and a greater 

 lateral compression, as compared with the Walrus now inhabiting 

 the seas of the northern regions. 



On the Specific Identity of Scomber pimctatus, Couch, with 

 S. scomber, Linn. By Francis Day, E.L.S. 



[Bead June 3, 1880.] 



(Plate VII.) 



In the ' Zoologist ' for 1849, Mr. Couch described a Mackerel, 

 which he had obtained the previous year in Cornwall, as " the 

 Dotted Mackerel," Scomber pimctatus. Prior to that period it 

 had not been observed, while since that time it has remained 

 unrecognized until April 21st this year, when I received a speci- 

 men from Mr. Dunn, of Mevagissey, in Cornwall, where it had 

 been taken the previous day. I was exceedingly gratified at ob- 

 taining this specimen (which was uninjured and quite fresh), as I 

 particularly wished to examine some of the species of British fish 

 which are least known and merely doubtfully admitted to the rank 

 of species. Pennant, ' British Zoology,' ed. 1776, and Fleming, 

 ' British Vertebrates,' merely record the " Common Mackerel " 

 (S. scomber) as existing in the British seas. Turton, ' British 



