TRIBE MYTILACEA.- 235 
M. Exzcans. Gray. Spic. Z. t. 6.f.14. Thin, slender, pel- 
lucid, pale green, posteriorly attenuated rounded, anteriorly dilated ; 
hinge margin straight, the anterior dorsal part finely rayed and 
transversely waved with purple, rest of the shell smooth. 13. 
Africa. 
M. Mercatrei. Nobis Z. P. 1844. Subtriangular-oblong, ven- 
tricose, covered with a yellowish brown epidermis, which is glossy 
except upon a narrow strip adjacent to the ligamental edge, and a 
lunule-like spot at the posterior end; anterior area much com- 
pressed, obsoletely bearded, reddish purple; posterior surface 
bluish white; umbonal ridge very prominent and obtusely subca- 
rinated near the acute and purple beaks; dorsal edge straight, much 
elevated, forming a distinct angle with the nearly straight and sub- 
equal anterior edge; anterior extremity rather attenuated and 
rounded ; ventral edge subcentrally incurved ; posterior extremity 
very narrow, short, but very prominent, and curving towards the 
beaks ; inside stained with purple anteriorly. 12..3. Philippines. 
M. Austrauis. Gray in King’s Australia. Inclined to oval, 
greatly attenuated and extremely short posteriorly, bearded, ven- 
tricose, under the tawny cuticle which becomes chesnut at each ex- 
tremity, the anterior slope purplish crimson; dorsal edge elevated, 
rather short forming an obtuse angle with the elongated anterior which 
is scarcely, if at all, incurved; ventral edge but slightly incurved : 
umbonal ridge only prominent near the narrow umbones: anterior 
extremity much produced but decidedly obtuse ; inside purplish. 
2..3.—Australia.—Shape intermediate between Modiolus and Tu- 
lipa. 
M. Purtrerinarum. Nobis Z. P.1844. Ovate-oblong, tumid, 
nearly smooth but bearded anteriorly, the cuticle of a tawny colour 
becoming darker atthe sides, and glossy excepting upon a lunule-like 
space at the tip of the rather prominent and rounded posterior ex- 
tremity ; dorsal edge elevated, but slightly convex, rather long 
forming a distinct but very rounded angle, with the nearly straight 
and slightly incurved anterior edge; ventral edge with a dilated 
incurvation; anterior extremity broad and rounded ; beaks narrow, 
the umbones elevated and the umbonal ridge very conspicuous ; 
within dark purple anteriorly. 24..4. Philippines. Somewhat 
like Modiolus. 
M. Biraprata. Nobis. Z. P. 1844. Oblong-triangular, ventri- 
cose, smooth, glossy, under a fulvous or brownish olive epidermis 
(which does not quite reach the nearly straight elongated and ele- 
vated hinge margin) reddish purple anteriorly, with a narrow white 
radiating streak beyond the very prominent umbonal ridge ; the 
shell from thence becomes pale brown with a pale ray just before 
the posterior extremity which is rather short, but prominent, very 
