A L G M. 175 



for its reception the genus Hemiptychus. In the Monatsbericht for 

 1849, he discards this name, in consequence of its prior application 

 to a genus of insects, and adopts the very appropriate and descriptive 

 name of Arachnodiscus, which was first used in .England, by whom 

 we are not informed. We find, however, that in Queckett's Histologi- 

 cal Catalogue, in the Museum of the Koyal College of Surgeons, pub- 

 lished in 1850, a species of this genus is given on the authority of 

 Mr. H. Deane. The present is a truly elegant species, and well worthy 

 to bear the name of the distinguished microscopist which we have 

 attached to it. It consists of discoid cylinders, adhering by their 

 circular bases to the fronds of various Algce, The discs are covered, 

 except near the centre, with large granules, disposed in concentric 

 circles. A small circular space in the centre is smooth, but is sur- 

 rounded by a series of elongated cells arranged in a radiating manner. 

 The beauty of the shell is much increased by a series of radiating 

 lines, commencing near the circumference, but not reaching the centre, 

 between which a shorter set is interposed, which in their turn have 

 one or more still shorter ones alternating with them. 



* Cocconeis rhombifer, Bail. & Harv. (Tab. 9, fig. 3, 4.) 



G. late elliptica vel suborbicidaris, Unea media oblique longitudinali 

 sigmoidea areolam glabratam dimidiante, quoe apice basique attenuata 

 est et versus umbonem in rhombi formam ampliata, superficie decus- 

 sation et transversim punctata. 



Lorica elliptical or nearly circular, and marked with a smooth, 

 central, sigmoid space, which widens in the centre, and assumes a 

 rhombic form. Surface minutely punctate, producing the appearance 

 of transverse and decussating striae. Abundant on Algce from Puget 

 Sound. 



* Cocconeis sulcata, Bail. & Harv. (Tab. 9.) 



G late elliptica vel suborbicidaris, transversim sulcata, sidck 30-40 

 arcuatis. 



A small species, somewhat resembling G. scutellum, Ehr., but dis- 

 tinguished by the distinct grooves upon the surface. 



ACTINOPTYCHUS SENARIUS, Ehr. 

 COSCINODISCUS OCULIS-VIRIDIS, Ehr. 



