148 J. WILFRID JACKSON ON 



The very wide range of this species is, in all probability, due to larval trans- 

 portation, as the larvae are known to live in a free and floating condition for nearly 

 a month, and have been taken in a drag-net not far from land (SCHUCHERT, 1911). 



Hemithyris sp. (PI. II. fig. 14.) 



Hob. Station 417 ; lat. 71 22' S., long. 16 34' W. (off Coats Land, Antarctica). 

 Depth, 1410 fathoms. March 18, 1904. Sea bottom, blue mud and stones. Tem- 

 perature 29 "9 F. 



Obs. Some fragmentary remains of a probable new Rhynchonelloid were met with 

 at the above station. These consist of hinge portions only of one ventral and two 

 dorsal valves, but are, unfortunately, too small and imperfect for accurate specific 

 description. 



The material at my disposal appears to belong to a small trigonal form possessing 

 a thin, translucent test. The colour is a yellowish-brown, and the outer surface smooth 

 with very faint growth lines. 



The ventral valve possesses dental plates, as in the type species Hemithyris 

 psittacea, and from the evidence of the fragment the beak appears to be somewhat 

 produced, and to possess a moderately large foramen. 



The dorsal valve exhibits a short, feeble, median septum separating well-marked 

 muscular impressions. There is no cardinal process. Hinge plate divided and 

 consisting of two short, flattened, curved lamellas, which are widely divergent. 



Shell-mosaic similar in character to but larger in size than that of R. cornea figured 

 by BLOCHMANN (1908 ; pi. xxxvii. fig. 16). 



Fig. 14 (PI. II.) in the present report is taken from a fairly well-preserved 

 fragment. 



The above description, of course, applies only to the posterior portion ; the anterior 

 end of the shell is quite unknown, hence one cannot say if the species is plicated 

 or not. 



Two new species of Rhynchonella (R. racovitzse and R. c/erlachei), and several 

 indefinite forms too imperfect for identification, have been described from the Western 

 Antarctic by JOUBIN (1901), but these all come from a less depth than the Coats Land 

 form. This latter may, however, be intimately related with one or other of these 

 forms, but owing to the paucity of material in both cases a decision on this point is for 

 the present out of the question. 



It is most unfortunate that the fragments of the Coats Lund example are so small 

 and indefinite, as this prevents a comparison being made, not only with the above- 

 mentioned recent forms, but also with the fossil examples of Hemithyris recently 

 described by BUCKMAN (1910) from Antarctica (Swedish Expedition), especially 

 H. antarctica, Buck., from the Pleistocene beds of Cockburn Island, off Graham Land, 

 to which species the Coats Land form presents some points of resemblance. 



(ROY. soc. EDIN. TRANS., VOL. XLVIII., 370.) 



