lid 



DESCRIPTION OF A NEW RISSOlD SHELL FROM 

 THE ANTARCTIC REGION. 



By J. COSMO MELVILL, M.A., D.Sc, and R. STANDEN. 



(Read before the Society, April 12th, 1916). 



Onoba cymatodes sp. nov. 



O. testa ?ninuta, albida, fusiforjiii, delicata, angusta, anfractibus /, 

 quorum apicales duo fceves, planati, fortasse in speciinine typico paullutn 

 detriti, cceteris apud medium iumescentibus, ad suturas multum 

 impressis, undique lotigitudinaliter costis flexuosis arete prceditis, et 

 spiraliter delicatissim'e et arctissime striatis, costis infra peripheriam 

 anfractus ultimi evanidis, apertura obtuse triafigulata, labro paullutn 

 effuso, columella obliqua. 



Long., 2*55 mm. ; lat., i mm. 



Hab. : Burdwood Bank, south of the Falkland Isles. Coll. : W. S. 

 Bruce, "Scotia" Expedition, 1905. 



This interesting addition to the Antarctic fauna had, unfortunately, 

 been accidentally omitted at the time of our writing the second 

 portion of the Mollusca of the Scottish National Antarctic Expedition.^ 

 It is, though so minute, a well-marked species, white, narrowly fusi- 

 form, whorls centrally tumid or ventricose, suturally much impressed, 

 seven-whorled, apex smooth and rounded, longitudinal riblets delicate. 



Onoba cymatodes sp. nov. 



close together, and slightly obliquely flexuose, while only with a lens 

 are the beautiful microscopic close spiral strise, generally diffused over 

 tlie surface, rendered perceptible. The mouth is obtusely, triangular, 

 a little recalling in this feature the considerably larger Rissoina 

 triangularis'^ Watson, from Cape York, North-East Au'Jtralia (of 

 which we also sifted a good example from shell-sand collected in Mag- 

 netic Island, Queensland, by Mr. Arnold U. Henn). 



After a prolonged search through a very large collection of this 

 family, belonging to one of us, we have found no near ally to our new 

 species, excepting Onoba carnosa Webster, 1905,^ from New Zealand. 



1 Trans. Royal Soc. Edinburgh, xlviii., part ii. (no. i8), pp. 333 sqq. 



2 Report "Challenger" Expedition, xv., p. 618, pi. xlvi., fig. 7. 



3 W. H. Webster, Trans. N.Z. Instit., xxxvii., p. 278. 



