Mollusks. 4315 



about forty miles. When the bank is gained, the South Knock, 

 or hill of Deskford, in Banffshire, is in a line with the Scar-naze or 

 head of Port Knockie, also in the same county ; and the North Knock, 

 a hill in Sutherland or Caithness, but not seen until nearing the 

 ground, is in a line with the town of Helmsdale, in Sutherlandshire. 

 These more strictly are the bearings of the west end of the horse- 

 mussel bank, which extends eastward some ten or twelve miles, until 

 it terminates at a place known to fishermen as the * Breadshell ' 

 ground ; so called, on account of the shells there found in a decayed 

 state, coloured or crumbling like bread. The breadth of the bank 

 from North to South is about six miles, and the depth of water over 

 it varies considerably, being in some places thirty or forty fathoms, 

 and in others only sixteen. The east end is the shallower or nearest 

 the surface, and from it the South Knock is seen on a line with Log- 

 giehead, which is on the east side of the town of Cullen." The 

 north-east coasts of Scotland are given as a locality for Modiola pha- 

 seolina of the ' History of British Mollusca,' but, so far as is known, 

 it has not been identified as a species found in the Moray Firth. 



Tumid-ribbed Crenella, Crenella discors. Common. " Among 

 the roots of Corallina officinalis, at Burghead, July, 1852," Mr. 

 Macdonald. Often found among shell-sand. Mr. Macdonald makes 

 the following remark upon the nomenclature of this species. Athough 

 quoted by the authors of the 'British Mollusca,' as a synonym 

 of their C. nigra, it is probable that the Modiola discrepans of Mac- 

 gillivray (Moll. Abred. p. 238) refers in part at least to this species. 

 " The large valve " and the " young individual from deep water," from 

 which the description appears to have been taken, may certainly be 

 referred to C. nigra ; but it can scarcely be doubted that those 

 " found in tufts of Corallina officinalis, growing in pools at the Cove," 

 were C. discors. 



Marbled Crenella, Crenella marmorata, {Modiola discors, Flem. 

 and Mac.) Common. " Occasionally free, adhering by its byssus to 

 shells, &c, but more frequently burrowing in the tough skin of Ascidia 

 sordida and A. intestinalis. " From a single individual of the last- 

 named, no fewer than five full-grown examples were taken on one oc- 

 casion," Mr. Macdonald. This species has also been taken from 

 Botryllus Schlosseri. 



Black Crenella or Corduroy Mussel, Crenella nigra, {Modiola dis- 

 crepans, Flem. and Mac. ?) Occasional. Two half-grown specimens 

 were found a few years ago at Stotfield. Mr. Macdonald has got 

 several very fine specimens and a few valves from the Buckie fisher- 



