Oeveral years ago I received through Professor S. Loven from the Swedish State 

 Miiseuin some samples af shellsand and mud, which had been collected during the ex- 

 pedition of the Roy. Swedish Fregate Eugenie 1851 53 on the Gallapagos Islands, 

 Honolulu, Port Jackson etc. On examining these samples, as well as many others, 

 received from various friends and correspondents, I found a number of diatoms, which 

 seems to me to be entirely new to science or at least of interest. Especially am I in- 

 debted to Dr. SoDERLUND for some very rich materials from the Mediterranean Sea and 

 the Balearic Islets, to Mr. Christian Febiger, the wellknown diatomist of Wilmington, 

 Delaware, Mr. Hauck of Triest, Prof. Berggren, Dr. 0. Nordstedt and others for va- 

 rious interesting gatherings. Mr. Gkunow of Vienna has kindly helped me in preparing 

 this paper and assisted me in many cases of uncertainity, and for which I here take 

 the liberty of tendering him my best thanks. 



Mastogloia Thwaites. 



1. M. imnduriformis Cl. N. Sp. 



Valve panduriform with cuneate ends. Margin with somewhat distant loculi, ex- 

 cept in the middle, on both sides of the central nodule, where they are wanting or 

 indiscernible. The surface of the valve is covered with small, irregularly scattered 

 ])uncta and very tine (20 in 0,01 mm.), parallel, punctate striae These stria3, which are 

 not strongly marked, cover the whole valve, except a small area, round the straight 

 median line and central nodule. Terminal nodules turned in opposite directions. 



Lcncrth 0,0975 mm. Breadth 0,027 mm. at the constriction 0,0195 mm. 



Gallapagos Islands (Eugenie Exp.) Very rare. 

 PL I, fig. 1, ^%. 



The outline of the frustule, the few and large loculi as well as its i)eculiar 

 structure destinguishes this tine form from all previously known species. Its nearest 

 allies are the Navicula; or Mastogloiie, forming A. Schmidts section Pseudodiploneis, 

 A', marginata Lewis, N. straiu/ulatd Grev., lU a stag I.? reliadatn GiiUN. 



