BIVALVIA. 



Mytiltjs edulis, var. ungulatus. 2nd Sup., Tab. VI, fig. 9 b. 

 Mytiitjs ungulatus, Linn. Syst. Nat., p. 1137. 



Locality. Cor. Crag ? Boy ton. 



The present figure, ungulatus, represents a specimen obtained by Mr. Charlesworth, 

 now in the cabinet of Dr. Reed ; this is said to be from Boyton, and from the colour of 

 the specimen, it most probably came from the Lower or Cor. Crag of that locality. 

 These two very different forms of this genus, galloprovincialis, and ungulatus, are now 

 generally admitted to be only variations of our common edible mussel, and I have 

 introduced them to show that they lived in the Crag Sea. They were both figured by 

 Dr. Jeffreys in the ' Mag. Nat. Hist.' for 1859, and at p. 10, ungulatus is there described 

 as an " unquestionably distinct species ;" but in his later work, the Brit. Conch., they are 

 considered as varieties of edulis, in which opinion I coincide. Pig. 20, Tab. II, of 

 ' Woodward's Geol. of Norfolk ' is another form of this variable species. 



Pectunculus pilosus, var. insubricus. 2nd Sup., Tab. VI, fig. 4 a, b ; Crag. Moll., 



vol ii, Tab. IX, fig. 1 d. 



Arca insubrica, Broc. Conch. Foss., sub. ap., p. 492, tav. xi, fig. 10 a, b. 



Locality. Cor. Crag, Sutton and Ramsholt. 



When figuring the shells of this genus in 'Crag Mol., vol. ii, tab. ix, I gave a 

 representation (fig. 1 d) of what I considered as an elongated variety of P. glycimeris,. 

 but this has since been given as a distinct species from the Crag, by Mr. A. Bell, as 

 P. insubricus. I have therefore now given a figure of its interior, and I am unable to 

 perceive any differences in this shell which justifies its separation from the general thick 

 solid form which has been called pilosus, beyond its slightly more elongated form, and 

 this may be connected with the more laterally extended form, common to pilosus, by 

 individuals partaking more or less of this elongated character. The recent shell called" 

 P. violacescens, presents precisely the same form, with hinge and denticles the same. 

 Fig. 5 a of Tab. IV is one of the laterally extended forms of P. glycimeris, from the 

 Coralline Crag of Sutton, obtained by myself. Fig. 5 b is that of a specimen of my own 

 from the Cor. Crag of Sutton, which seems to agree with that figured by Brocchi, 

 ' Conch. Fos. Sub-Ap,' p. 483, Tab. II, fig. 8, under the name of nummarius. Fig. 4 b 

 represents the inner lining of one of my specimens which separated itself; and as it 

 corresponds with a figure given by Phillippi, ' En. Moll. Sic.,' Vol. II, Tab. XVIII; 

 fig. 10 a, 6,1 thought it best to have it here figured. 



