110 THE EOTIFERA. 



aquarium, in Septombcr 1854. Its manners agreed witb those of the larger Coluri, 

 shutting itself within its valves, and that so stubbornly, as to die rather than open 

 them. Lately I have received specimens from Mr. Hood, found in marine tide-pools in 

 the Firth of Tay ; and have taken many in Torbay. 



Length. Of lorica, ^i^ inch ; of foot and toe, g|^ inch ; total extended, ^^ to ^ijj inch. 

 Habitat. Marine pools in Forfarshire and Devonshire ; domestic aquarium (P.H.G.). 



Very recently specimens of what I suppose M. clulcis, Ehr., have been sent me, 

 from fresh water, by Mr. Lord of Eawtenstall. The lorica is acute, instead of obtuse, 

 behind.— P.H.G.l 



Genus MYTILIA, Gosse, gen. nov. 



[GEN. CH. Body ovate ; lorica as in Colurus, but the head and neck hahitiudly 

 protruded, as tvell as the ivhole foot ; no frontal hook. — P.H.G.] 



M. TAviNA, Gosse, sp. nov. 

 (PI. XXVL fig. 8.) 



[SP. CH. "Eyes tivo, frontal, loide ajMrt. Marine. 



The lorica is essentially similar to that of Colurus (though the facies of tlie animal 

 is quite different), being a shell of two lateral valves, like that of a mussel, unbroken 

 on the dorsum, descending on each side, and open all along the venter. Behind they 

 are patent, where the thick foot emerges ; but their edges approach, or even overlap, as 

 in Pterodina, at the pectoral front. A massive head, and an equally thick, distinct neck, 

 both about equal to that part of the trunk that adjoins them, are normally projected 

 from the lorica, and not, as in Colurus, concealed between the valves. As there is, 

 moreover, no trace of the hood, or hooked plate, that shields the face in kindred forms, 

 the difference of aspect is very marked, and one of the Illoricate forms is involuntarily 

 suggested.' This is augmented by the circumstances, that the foot is long and thick, 

 especially at its base, that it tapers there gradually from the thickness of the trunk, and 

 that it is habitually carried in the line of the body. Whereas, in Colurus and Monura, 

 it is much smaller than the visible body, is usually projected at a sensible angle, and 

 appears to come out between the ventral edges of the valves. The lorica, too, is of 

 much less depth in proportion to its length ; for, whereas, in Colurus the depth to the 

 length may be about 2 : 3, in Mytilia it is about 2:5. It is obliquely truncate at the 

 hind margin, the lateral edges diverging thence till they meet at the pectus. The body, 

 which is arched on the dorsum, diminishes along the lumbar line, and forms a minute 

 conical projection, rej)resenting a true tail, behind which the cloaca opens, whence the 

 foot proceeds, in a similar ratio of diminution and in the same line, for a considerable 

 length, terminating in two stout pointed toes, often jerked widely apart. Each is per- 

 meated by the usual mucus-gland, long, thick, and clavate. The internal structure is 

 with difficulty defined. The extreme restlessness of the creature, combined with its 

 minuteness, renders an examination during life almost impossible ; and, after death, the 

 outlines of the delicate organs become blurred, and soon obliterated. I believe I have 

 perceived, on repeated occasions, and in many specimens, two minute eye specks at the 

 front, rather wide apart. The mastax is comparatively large, and the tropin normal 

 (as in fig. 8c). But the whole interior is almost opaque from granulation, and so, very 

 difficult to penetrate. 



It is a pretty little creature, sprightly and attractive, with much in its manners and 

 ways that reminds us of its kindred Coluri, one of which, C. amhlytelus, is its constant 



' I cannot avoid a lurking suspicion that under Ehrenberg's figure of Distcmma marinum may have 

 lain Mytilia tavina, notwithstanding discrepancies. 



