196 "TERRA NOVA" EXPEDITION. 



position. There is a slight pseudopedicle-eollar, i.e., a thickened rim inside the 

 foramen for muscular attachment. 



Internally both valves are smooth, and no dental plates are present. In the dorsal 

 valve the cardinalia consist of two divergent and high-standing socket-ridges with 

 hinge-plates extending inwards and meeting in the median line over the septum. The 

 crural bases are slightly discernible on the surface of the plates and are separated from 

 the socket-ridges by slight intervals. The inner hinge-plates descend sharply from the 

 crural bases to the septum, forming a rather deep trough. A bulbous cardinal process 

 is present at the apex of the trough. The mesial septum is sharp-edged and extends 

 to rather more than a third the length of the valve. Compared with the typical 

 Magellaniform type of cardinalia, as displayed by M. j1<tve.wm, the chief difference lies 

 in the steepness of the inner hinge-plates. In consequence of this the mesial septum is 

 not as high as in M. flavescens. 



In somewhat younger specimens in the "Terra Nova" collection the cardinal 

 process is not so large and prominent, and the hinge-plates are much thinner. Each 

 hinge-plate, too, is clearly divided into two parts by the well-defined crural bases which 

 run independently from the umbo. The type of cardinalia here recalls that seen in 

 several Dallinoid forms. 



In the "Discovery" and "Terra Nova" examples the descending branches of the 

 loop do not curve outwards as much as in M. fl<i recent. 



The number of punctse per square millimetre in the " Discovery " specimen is 60 ; 

 in examples from Station 355, 50-65. On the external surface the punctae in the 

 latter specimens are slightly oval ; on the inside they are rounder and measure 

 45-55 X 70-80 /^. They are arranged in transverse rows, more or less parallel to 

 the contour of the shell. 



Up to the present this species is only known authentically from the neighbourhood 

 of the type-locality. Eichler [1911, p. 93] refers to a specimen found amouo- the 

 material dredged by the Swedish South Polar Expedition, in the Magellanie region, 

 as iu all probability possessing affinities with M. /'/<//////*. The size of the punctse, 

 however, seems to suggest that it may be an entirely new species of Mdyellnnia 

 [cf. Blochmann, 1912, p. 9, pi. i, fig. 15]. 



Smith, in describing this species, remarks upon its close alliance with the 

 Patagonian Magellania c<'iix<i of Solauder, and more especially with the M. 

 kerguelenensis of Davidson. In fact, it was with some hesitation that he ventured 

 to separate it specifically. It is, however, clearly distinct, in my opinion, from 

 either of these species, both externally and internally. From the latter species it 

 ditt'ers entirely in type of cardinalia. Judging from specimens in my collection, 

 dredged oft' Kerguelen Island in 150 fathoms, ^f. kerguelenensis appears to possess a 

 peculiar type of cardinalia, which is somewhat different from that of tvpical J/</'/(7A//// 

 and Terebratella. It has a thickened septum, apparently extending to the apex, 

 slight hinge-plates descending to a callus-deposit in the umbonal area, and thick 



