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

 Museum 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. Södeelund 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. O. Nordstedt and others for va- 

 rious interesting gatherings. Mr. Geunow of Vienua 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. panduriformis 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 

 puncta and very fine (20 in 0,01 mm.), parallel, punctate striaj. 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. 



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



Gallapagos Islands (Eugenie Exp.) Very rare. 



Pi. I, fig. 1, ^°7i. 



The outline of the frustule, the few and large loculi as well as its peculiar 

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

 allies are the Naviculaä or Mastogloia', forming A. Schmidts section Pseudodiploneis, 



iV. marginata Lewts, N. atrangulata Grev., Mastogl.f reticulatn Grun. 



