OF THE ETTPODTSCEJE. 



845 



stone. Disc small under a low power, 

 bluish, with a darker, brownish border. 

 The granules, which, according to Mr. 

 Norman, are about 17 in -001", are so 

 regularly arranged as to form concentric 

 circles as well as radiating series. A. 

 Broivneii agrees in colour with A. Ore- 

 ffamcs, but in the arrangement of its 

 granules more resembles A. Beeverim. 

 From the former it differs in the regidar 

 radiant arrangement of its granides, 

 smaller size, fewer processes, and much 

 flatter surface. From A. Beeverice it is 

 distinguished by its colour and closer 

 granules. 



A. Or eg anus (Bailev). — Disc coloiu-ed, 

 with circidar perforation-like umbilicus, 

 convex centre, flattened border, short 

 cylindi'ical slightly emarginate marginal 

 processes, and series of minute crowded 

 granules. Bail. Proc. Acad. Philadelphia, 

 1853 ; Grev MJ. vii. p. 156, pi. 7. f. 2. 

 California, both recent and fossil ; Mon- 

 terey stone, Puget's Sound. This very 



distinct species is easily recognized by 

 its colom-ed disc and cylindrical emar- 

 ginate processes, which are from 6 to 27 

 in number, and close to the margin. 

 Under a low power its minute granules 

 appear an-auged in waved or oblique 

 lines, but imperfectly radiant under 

 higher powers. (yi. 4.) 



A.. pulcher (^OYm?in, MS.). — Disc large, 

 colom'ed, with from 7 to 16 marginal 

 processes ; central gi*anules in-egularly 

 scattered or crowded, the others in di- 

 stinct, close, radiant rows. Fossil. Mon- 

 terey stone. A. pulcher agrees with A. 

 Browneii in its coloured, slightly and 

 uniformly convex disc and radiant ar- 

 rangement of granules. It differs from 

 that species by its much larger size and 

 more numerous processes. The most 

 remarkable feature of this species is its 

 I granulose centre, in which respect, as 

 ' well as in its radiant granules, it differs 

 fi-om A. Oreganus. Granides 12 in -001". 

 (\^ii. 28.) 



Genus ArLISCUS (Ehr., Bail.).—" Fnistiiles cylindrical or discoid ; lateral 

 surfaces undulated, having two circular, flattened, mastoid, imperforate pro- 

 cesses at some distance from the margin ; umbilicus (generally present) 

 smooth, circular, surrounded by a plumose arrangement of dots and lines ; 

 sides smooth" (BC. 1854.). 



" The projections on one valve are usually on a line at right angles to that 

 on which those of the opposite valve are placed " (B.). Xiitzing unites Auliscus 

 'with Coscinodiscus ; but it seems more nearly allied to Eupodiscus. 



* Disc with a conspicuous circular 

 umhilicus. 



Ariuiscvs pruinosus (B.). — " Disc with 

 four sets of curved and sparsely pimc- 

 tate lines, two diverging from the large 

 smooth umbilicus, while the other two 

 converge round the large processes." 

 BC. 1854, pi. 1. f. 5-8. Ptecent. United 

 States. (VI. 1.) " Frustules large, discoid 

 or cylindrical ; edges bevelled, central 

 portion in front view smooth or vrith 

 longitudinal parallel lines " (B.). We 

 have seen frustides of this species with 

 3 processes. 



A. punctatus (B.). — Frustules like 

 those of A. pruinosus, but their lines so 

 crowded and closely punctate that the 

 plumose aiTangement is scarcely visible. 

 BC. pi. 1. f. 9. United States. " This 

 may prove a variety of the preceding; 

 but the sparsely punctate surface of the 

 one and the closely punctate sm-face of 

 the other appear to offer a sufiicient 

 distinction between them" (B.). 



A. ccelatus (B.). — Disc with unequal. 



the margin towards the centre, but 

 lea\dng a well-defined central, four- 

 lobed or cruciform figure, with waved 

 lines radiating in four sets from the 

 umbilicus. BC. pi. 1. f. 3, 4. In sand 

 from West Indian sponge, and in sound- 

 ings fi'om Mobile Bay. Umbilicus di- 

 stinct, smooth, the lines proceeding from 

 it towards the processes in converging 

 cm-ves, the others variously flexed and 

 anastomosing. 



2 * Umhilicus wanting or obsolete. 



A. scfilptus (Smith). — Disc with im- 

 equal, sti'ongly marked short lines, radi- 

 ating inwards from the margin and 

 leaving a weU-defined ceuti-al, four- 

 lobed space, marked with fom- sets of 

 fainter lines radiating from the centre. 

 =■ Eupodiscus sculptus, SBD. i. pi. 4. f. 42 ; 

 Bri M.I. ^dii. p. 94, pi. 5. f. 3. England, 

 (vi. 3.) This species resembles A. cce- 

 latus, but has no umbilicus. We have not 

 seen the striae of the central quatrefoil so 

 strongly marked as in Professor Smith's 



strongly marked lines proceeding from i figure, but always much fainter than the 



