46 SECOND SUPPLEMENT TO THE CRAG MOLLUSCA. 



represented. It is suborbicular or slightly oblique, subequilateral, and much flatter 



than the ordinary form : the exterior is covered with the same 

 radiating fine striae, decussated by lines of growth, as are present 

 on the ordinary form, with which also its dentition is identical; 

 and it possesses the same impression or siphonal scar which is 

 characteristic of L. Lajonkairii. As the differences presented 

 by the present shell consist only in its greater flatness and 



Lucinopsis Lajonkairii, Payr. different outline, I have regarded it as an accidental variety 

 var. subobiiqua, s. Wood, only ; but if a series should be obtained maintaining these 



characters, they might be regarded as of specific value, and the above name, subobiiqua, then 



be assigned specifically. 



ASTARTE MUTABILIS, S. Wood. 2nd Sup., Tab. VI, fig. 1. 



ASTARTE MUTABILIS, S. Wood. Crag Moll., vol. ii, p. 179, tab. xvi, fig. I. 



Diameter, 2 inches. 



Locality. Cor. Crag, near Orford. 



I have had the present specimen figured for its great size, showing the margin 

 without crenulations. This freedom from crenulation has always been considered by 

 myself a distinguishing mark denoting that the animal which formed the shell had not 

 arrived at maturity, and I can see no reason against such a supposition. This is as 

 large as the largest of any specimens I have of this species, and larger than many which 

 have the margin ornamented with crenulations. So far as I have studied the shells of 

 the genus Astarte, I have always found the young or immature specimens of a species, 

 that is decidedly crenulated when full grown, to be without that peculiarity. 



In the plate of the "Arctic Shells/' in Sir E. Belcher's 'Arctic Voyage,' are the 

 figures of two species of Astarte. Eig. 7 a, 6, of Tab. XXXIII, is named and described 

 as new under the name of A. Rickardsoni. This is stated by Dr. Jeffreys, in ' Ann. 

 and Mag. Nat. Hist.' for 1877, p. 234, to be the same as A. crebricostata of Eorbes, 

 but unless the figure given in Belcher's work be erroneous, it seems to me to be the 

 common form of Astarte borealis, such as occurs in the East Anglian beds ; while 

 fig. 5 a, b, of the same Tab., called A. fabula t answers to the shell figured and described 

 from the Red Crag as A. crebrilirata, 'Crag Moll./ vol. ii, p. 184, tab. xvi, fig. 2, and 

 which would thus appear to be living in the Arctic seas. 



