Dr. G. C. Wallich on the Structure of the Valves of Diatoms. 351 



pheriam angulato ; apertura semiovata ; labio recto, acuto ; um- 

 bilici margine cannula acuta circumciucto. 



Hab. Seto-Uchi; Akasi; 15 fathoms. 



A small white species from the Inland Sea of Japan, with the 

 margin of the wide umbilicus encircled by a narrow elevated 

 keel. 



Genus Stenotis, A. Adams. 



Testa compressa, elongato-ovata, auriformis ; spira brevi, acuta ; 

 anfractibus planis, simplicibus, ultimo sejuncto. Apertura oblouga, 

 postice angustata ; peritremate acuto, recto, coutinuo, integro. 



I have founded this genus on a little shell which I obtained in 

 the Inland Sea of Japan, and also at Yobuko, a small harbour on 

 the west coast of Kiusu. It possesses some of the characters of 

 Fossar, and reminds one of Vanikoro : in form it resembles 

 somewhat a minute Naticina ; but perhaps its true relations are 

 with Lacuna, although the members of that family are littoral 

 in their habits. 



Stenotis laxata, A. Adams. 



S. testa elongato-ovali, compressa, tenui, sordide alba ; spira parva, 

 acuta ; anfractibus 3, planiusculis, rapide crescentibus ; anfractu 

 ultimo magno, soluto, antice dilatato ; apertura auriformi, postice 

 angustata ; umbilico patulo, margine angulato. 



Hab. Idsuma-Nada ; 17 fathoms. Yobuko, west coast of Kiusu j 

 14 fathoms, mud. 



XL. — On the Structure of the Valves of Pleurosigma and other 

 Diatoms. By G. C. Wallich, M.D., F.L.S., F.G.S., &c. 



In a scientific point of view, it is obviously immaterial whether 

 the markings on a Diatom-valve present this or that configura- 

 tion, or whether minute points on its surface consist of eleva- 

 tions or of depressions. At all events, the physiology of the 

 Protophytes, so far as we have heretofore become acquainted 

 with it, does not appear to have been advanced a single step by 

 the fitful controversy that has taken place on the subject, with 

 no better result than that of rendering it distasteful to the 

 generality of scientific readers. 



But, notwithstanding this, it cannot be denied that the 

 accurate determination of the nature of these markings is of 

 great importance indirectly, that is to say, by furnishing a 

 standard wherewith to gauge the powers of our highest optical 

 combinations, and enable us to pronounce with some approach 

 to confidence when minute appearances are, or are not, illusory. 

 In this sense the subject may be regarded as bearing essentially 



