198 "TERRA NOVA" EXPEDITION. 



The lieuk has rounded Hanks and is strongly incurved over the umbo of the 

 dorsal valve, almost hiding the conjoined deltidial plates. The foramen is circular 

 and of moderate size. 



The above and other specimens from the various Stations exhibit very clearly 

 through the test the vascular sinuses in the pallium. 



In the ventral valve there are four of these in the mesial portion ; the two inner 

 sinuses are straight and slightly divergent ; the two outer curve slightly outwards and 

 possess two or three simple ramifications on their exterior sides. 



In the dorsal valve two sinuses only are present. These pass alongside the 

 adductor muscles, and then diverge outwards slightly. Each bears two simple 

 ramifications on the exterior side. 



In both valves the sinuses cease abruptly some distance from the shell-margin, no 

 ramifications being present at the extremities. 



The vascular sinuses in general are very much simpler than those of M<i//<'/Ii/ii/n 

 venom, figured by Fischer and Oehlert [1892, pi. 12, figs. 5, 12, 13 and 15]. 



The foregoing description of the external features of this species applies generally 

 to the majority of the smaller adult specimens in the "Terra Nova" collection, and to 

 others obtained by the " Discovery " Expedition, received on loan from the British 

 Museum for purposes of study and comparison. In some cases the shells show a 

 pointed front ; in others, of equal size, a truncated front. 



In the younger examples the shells are either quite circular or slightly pointed 

 anteriorly. The growth-lines, too, are not so conspicuous or so numerous. 



The interior of both valves is concentrically sulcate, like the exterior. In the 

 ventral valve the teeth are moderately strong and situated at the basal angles of 

 the deltidial plates : there are no dental plates, but a slight pseudopedicle-collar 

 is present. 



In the dorsal valve the cardinalia and the adult loop are of the Magellania type. 

 The branches of the loop, however, are not as narrow as in Miii/i'l/nn/n flavescens, the 

 ascending branches especially being broad, both in adult and earlier stages. Eichler's 

 figures [1911, pi. 44, figs. 23-24], of a specimen in a Terebratelliform loop-stage, show 

 this feature clearly. This character has led Hedley [1911, p. 114] to consider the 

 species as belonging to his genus Campages, but I am unable to agree with this 

 conclusion.* There is a thin acute mesial septum extending from the centre of the 

 valve back to the hinge-plates, under which it runs to the apex. The hinge-plates 

 consist of two lamellae extending from the socket-ridges to t lie median line over the 

 septum. Each plate is distinctly separable into two parts by the crural bases, which 

 are clearly visible on the surface running from the umbo. Unlike ^f. flavescens, the 

 brackets (which form the dental sockets) do not reach inwards to the crural liases. In 



* Hedley also places in Cniupdijes the South Australian Nui/am-Un jaffaensis, Bl., but from his i 

 it is obvious that this species possesses a different type of ivmlinalia from the genotype, C. furdfera, 

 Hedley. 



