TUKTONIA. 83 



extremity of the ligament in each valve, which may pos- 

 sibly be regarded as such by some individuals. There 

 appear to be two primary teeth in each valve, but so close- 

 ly adjacent, as almost to resemble a single complicated one. 

 In the right valve, the lunular or foremost one is strong 

 and subtriangular, the other, which lies under the middle 

 of the umbo, is somewhat smaller ; in the left valve the 

 central tooth is the larger, and is conic and erect, the 

 lunular one being the less conspicuous, inclining forwards, 

 and, as well as in the right valve, somewhat laminar. The 

 ligament is not really internal, yet is not visible until the 

 valves are opened, lying as it does between the hinder dor- 

 sal edges without projecting externally. The length of 

 this minute shell rarely exceeds the twelfth of an inch, and 

 its breadth is but a trifle more than half that measure- 

 ment. 



All we know of the animal is contained in the generic 

 character, due to the observations of Mr. Alder. It in- 

 habits pools and crevices of rocks between tide-marks, 

 usually high up, often in company with Kellia rubra. 

 Adhering to corallinse from the rocks of the little islet of 

 Herni near Guernsey (S. H.) ; at Scarborough it is com- 

 mon in the roots of the Chondrus crispus (Bean) ; it is 

 likewise captured in Northumberland (Alder) ; Whitesand 

 Bay in South Devon (Jeff, cab.) ; Exmouth (Clark) ; Fal- 

 mouth (Jeffreys) ; abundant among the roots of CoralUna 

 officinalis and Lichina, near high water-mark on slate rocks 

 in the Isle of Man (E. F.). At the roots of Lichina 

 pygmaa, Oxwicli and Langland Bays in Glamorganshire 

 (Jeff.) ; Tenby (Lyons). 



In Ireland it is found in Cork harbour (Humphreys) ; 

 Portmarnock, Belfast (Jefli". cab.) ; and is indeed " abund- 

 ant on the north-east coast, in the stomachs of Mullets " 



