52 MOLLUSCA FROM THE CRAG. 



Two fragments were found by myself in the Coralline Crag at Gedgrave, which 

 belong undoubtedly to this genus, and as far as can be determined from their muti- 

 lated condition, appear to be of the above-named species ; they are introduced here 

 provisionally until better specimens be procured than what I possess : my specimens 

 of the left valve have an obtuse tooth immediately under the beak within the 

 ligamental margin, and are beautifully nacreous within. The area for the ligament 

 appears somewhat larger than is shown by the recent shell. 



MYTILUS,* Linnaus, 1758. 



MYTULUS. Rondelet, 1555, sec. Herrm. 

 MUSCULUS. List. 1687. 

 MITULUS. Browne, 1756. 

 PERN A (sp.). Adans, 1757. 

 Id. Schum., 1817. 



CALLITRICHE et CALLITRICODERMA. Poli., 1795. 



Generic Character. Shell equivalve, inequilateral, oblique, elongate, wedge-shaped 

 or subtriangular, more or less tumid, sometimes thin and semitransparent, occasionally 

 thick and opaque : in the recent state covered with an epidermis : umbones acute, 

 terminal ; hinge slightly denticulated ; surface generally smooth, sometimes striated. 

 Ligament linear, internal. Muscular impressions two, unequal, anterior one near the 

 umbo, elongate, posterior one suborbicular near the posterior part of the ventral 

 margin ; palleal impression without a sinus and rather obscure. 



Animal elongate, with the lobes of the mantle partly fringed, disconnected except 

 at the posterior, where there is a short anal siphon : adductor muscles very unequal ; 

 a cylindrically formed foot furnished with a gland and groove. 



Animals belonging to this genus are inhabitants of salt-water or estuaries, and are 

 generally very littoral in their habits ; the common Mussel, as is well known, is more 

 often found where it is deserted by the retiring tide, but some are inhabitants of the 

 sea at a considerable depth. The living species are found in various parts of the 

 world, and in the fossil state have been obtained as low in the secondary series as the 

 Cornbrash. 



MYTILUS EDULIS, Linnaus. Tab. VIII, fig. 9, a e. 



MUSCULUS SUBC.&RULEUS. List. Hist. Conch., lib. iii, fig. A, 200, 168/. 

 MYTILUS EDULIS. Linn. Syst. Nat., ed. 12, p. 1157, No. 253, 1767. 



VULGATISSIMUS. Chem. Conch. Cab. viii, p. 169, t. 84, figs. 750, 751, 755. 

 PELLUCIDUS. Penn. Brit. Zool., ed. 4, vol. iv, p. 112, pi. 63, fig. 75. 

 VULGARIS. Da Costa. Brit. Conch., p. 216, pi. 15, fig. 5, (left-hand fig.) 

 INCURVATUS. Penn. Brit. Zool., pi. 64, fig. 74. 

 ELEGANS. Brown. Illust. Conch. Gr. Brit., pi. 29, figs. 14, 15, 1827. 



* Etym. fjivriXos (deriv. a /uws, as vavnXos a voDs). 



