I 



MoUusca from the North-west Falklands. 131 



This agglomeration was found spread over a boulder-stone, 

 exposed at low tide in the upper portion of Roy Cove Creek, 

 on January 14th, 1910. There must hava been thousands of 

 tliese little mollusks imbedded thus, for upon removing it 

 from the I'ocks on which it was spread the effect was that of 

 little white stars or points of light, sometimes iridescent. 

 ]\liss Wigglesworth, of the Manchester University, has 

 kindly examined and analyzed this Algoid mass, and pro- 

 nounced it mainly to consist of the cosmopolitan Chlorosperm 

 alga Enteromorpha compressa, with a species of Conferva. 



CXAMIONEMA, subgen. nov. 



Cyamium [Cvamionema) decoratum, sp. n, 

 (PI. VII. figs. 5, 5a, oh,) 



C. testa parva, delicatissima, papyracea, alba, fequivalvi, inaequi- 

 laterali, umbonibus contiguis, margine dorsali recto, ventrali fere 

 parallelo, latere antico rotunda extenso, postice truncatulo, 

 superficie concentrice undique irregulariter striata, saepe perio- 

 straco tenui olivaceo-stramineainduta, ab umbonibus ventralem ad 

 marginem centraliler oblique filoso-lirata, lirisnumero 7-8, pagina 

 intus alba; valva dextra duobus dentibus parvis contiguis iustructa, 

 sinistra uno dentemajore prominulo, lateralibus omnino evanidis, 

 ligamento interno nuUo, externo perlougo. pallide stramineo, linea 

 palliali Integra. 



Alt. 3, lat. 5 mm., sp. max. 



Hah. N.W. Falklands, b-^ June, 1910. 



Tiiis is a very delicate white shell, of extreme fragility, so 

 much so that nearly all the specimens have been fractured 

 in the course of microscopical examination. In several 

 Avays we consider it difFeis from the normal Cyamium^ 

 and justification for the creation of the proposed subgenus 

 appears, we think, firstly, in the absence of the internal 

 ligament ; secondly, in dental disposition, the right valve 

 containing two small contiguous teeth, the left only one, but 

 that larger and more conspicuous, the lateral teeth in either 

 valve appnrently absent altogether ; and, thirdly, in the 

 external sculpture, both valves being ornamented, in addition 

 to the concentric lines, with seven or eight thread-like liiaa 

 proceeding radiately from the umboes to about the centre of 

 tiie ventral margin. From this circumstance the name Cya- 

 mionema is suggested — Kvajxiov and vrjfjba, a thread. 



We would here especially thank Mr. A. J. Jidves-Browne, 

 F.R.S., for his examination of this interesting shell and his 

 comments thereupoti. Several new species of Cyamium have, 

 during the past few years, been described by Mr. H, B. 

 Preston and other?, but none seem comparable with the one 



