802 Transactions of the Society. 



published by the Society in June of the present year ; but in addition 

 to the names there recorded, I would here express my p;i-atitude to 

 Dr. A. C. Macrae and Mr. A. de Souza Guimaraens, for the liberality 

 and readiness with which they have placed at my disposal the resources 

 of their cabinets, and to the former for verbal summaries which he 

 has from time to time given me of his extensive observations on the 

 distribution of the Diatomaceae in the Indian Ocean and Eastern 

 Archipelago. 



AULISCUS Ehrb. emend. 



AuLiscus Ehrb. emend., Mon. Ber. Ak., 18i3, p. 270. 



Valves circular, subcircular, or elliptical, rarely obtusely angular. 

 Surface almost flat, or rising from central space to processes ; trans- 

 verse areas at right angles — rarely oblique — to line of processes 

 frequent, flat or rising towards, and widest at the outer ends ; obconical 

 or obcordate areas between central space and processes often distinctly 

 defined ; the central portion of the valve between the processes some- 

 times sharply circumscribed, regularly rounded, elliptical, protuberant, 

 or constricted opposite the central space, sometimes extending to the 

 outer side of the processes, rarely much elevated. Colour pale to pale 

 smoky grey, rarely dark grey or bluish. Central space circular, ellip- 

 tical, obtusely angular or diamond-shaped with concave sides and pro- 

 truding angles, hyaline, distinct or inconspicuous. jMarkings minute, 

 punctate, in delicate continuous or pruiuose striae, sometimes forming 

 wider, straight or curved, continuous or interrupted strands, those 

 strife converging to central side of processes usually distinct ; rarely 

 large, areolate, pearly, and without order ; interspaces hyaline ; apiculi 

 irregularly scattered outside of central space and processes, or confined 

 to more definite bauds, sometimes few or absent ; a reticulum with 

 delicate, small or large, coarse, subequal or irregular meshes extending 

 from central space to border or confined to central portion only, more 

 rarely only outside of central portion, sometimes present. Processes 



Plate XV. 



Fig. 1. — Pseudauliscus ambiguus var. major nov. x 660. 



„ 2. — Auliscus convolutus sp. n. X 660. 



„ 3. — Pseuduuliscus hirsutus sp. n. x 660. 



„ 4. — „ anceps sp. n. x 660. 



„ 5. — Auliscus caelatus var. delicatula nov. x 660. 



„ 6. — „ „ var. mutabilis nov. x 660. 



„ 7. — „ „ var. picta nov. x 660. 



„ 8. — „ „ var. coDstricta nov. x 660. 



„ 9. — „ „ var. impressa nov. x 660. 



Plate XVI. 



„ 1. — Auliscus decoratus var. affinis nov. x 660. 



„ 2. — „ elegans var. subpunctata, nov. x 660. 



„ 3. — ,, c«latus var. tenuis nov. x 660. 



„ 4. — Isodiscus mirificus x 660. 



„ 5. — Auliscus intermedius var. simplex nov. x 660. 



„ 6. — „ cselatus var. protubeians var. nov. x 660. 



„ 7. — Pseudauliscus rotalus sp. n. x 660. 



