OF THE COSCINODISCE^ , 



839 



in Silliman's Amer. Joiirn. 1852.) " The proximate genera^ Asterolampra 

 and Asteromphalus, are readily distinguished. In the former, all the connect- 

 ing hnes are symmetrical; in the latter, two are parallel;" whilst in this 

 genus one line divides half-way from the centre and proceeds to two of the 

 compartments, the smooth ray between which is smaller than the others, but 

 not parallel as in Asteromphalus. 



AsTERODiscus JohisonH. — Kays and 

 mnbilical divisions from five to nine. 

 Bermuda earth. This includes the fol- 

 loAviiig species of Johnson : — 



A. quinarius. — Marginal rays and um- 

 bilical divisions five. 



A. senarius. 

 bilical divisions six. 



-Marginal rays and um- 



A. nonarius. — Marginal rays and um- 

 bilical divisions nine. 



" Front view bi-convex ; compart- 

 ments elegantly marked with minute 

 dots, arranged in excentric cmwes '' 

 (Johnson). 



Genus ACTIXOPTYCHUS (Ehr.).— Frustules disciform, ceUulose ; disc 

 divided into equal triangiilar compartments by lines or internal septa (E.). 

 = Actinocyclus, Smith, not Ehr. The circular disc is cellulose, and divided 

 into triangular portions by lines ('' internal septa," E.) radiating from its 

 centre. The alternate portions are usually more distinct, owing to the undu- 

 lated form of the frustules, which causes them alternately to be nearer to or 

 more remote from the eye. The apparent septa distinguish it from Actino- 

 cyclus, and the absence of spines from Heliopelta and Omphalopelta. We 

 have not the slightest doubt that Ehrenberg has properly separated Actino- 

 cyclus from Actinoptychus. Professor Smith himself practically admits this, 

 by placing the groups in different genera, although he has not retained the 

 names as affixed by their author. If, however, the validity of their separa- 

 tion be admitted, the founder of these genera has surely an undoubted right 

 to retain the original name for whichever group he thinks fit. Professor 

 Smith seems to have erred by choosing as the type of Actinocyclus, not one 

 of Ehrenberg' s species, but a form placed in that genus by Professor Kiitzing, 

 though really belonging to Actinoptychus. 



AcTixoPTYCHUS temcinus (E.). — j and minutely punctate^ and which has 

 Disc with 3 or 5 radiating lines, -^dth- j been described as a new species by Mr. 

 out a distinct umbilicus ; compartments " " 



even. KB. pi. 1. f. 19. =^. quinarius, E. 

 Fossil. Virginia. The rays proceed 

 directly to its centre, without leaving an 

 umbilical space. 



A. unduhtus (Kiitz.). — Disc with its 

 compartments alternately prominent and 

 cellulose and depressed and punctate; 

 umbilicus indistinct or indefinite. = 

 Actinocyclus unduhdus, KB. pi. 1. f. 24 ; 

 Actinoptyclms hiternarius, EM. pi. 18. 

 f. 20 ; A. hiternatus, EM. pi. 35 a. 16. f. 1. 

 (v. 88.)' America. Guano, &c. Com- 

 partments six or more. 



A. velatus (E.). — Compartments six, 

 loosely ceUulose ; surface apparently 

 covered by a thin pimctated membrane. 

 KSA. p. 130. Virginia. We are imac- 

 quainted with this species, but think it 

 may probably be a state of A. undulatus, 

 the valves of which frequently consist 



Roper in TM. vi. p. 23 {Actinocyclus tri- 

 radiatus), who first observed it detached 

 from the true valve. He and others 

 have since found the plates in situ. 



A. senarius (E.). — Compartments (6 

 or more) alternately prominent, all 

 loosely celhdose ; umbilicus angular, 

 definite ; rim striated. EM. various 

 plates. = Actinocyclus tindulatus, SB. i. 

 pi. 5. f. 43. (IX. 132.) Common, both 

 recent and fossil. Mr. Tuffen West re- 

 gards A. senarius and Omplialopdta areo- 

 lata as identical. The presence of mar- 

 ginal spines in the latter seems indeed 

 the only essential distinction; and we 

 have generally succeeded in detecting- 

 spines, more or less distinct, exactly 

 such as Professor Smith has represented 

 in one of the figures of his Actinocyclus 

 iindidatus. The determination of species 

 in Actinopts'chus is very difiicidt. The 



of two dissimilar plates, one having the number of the compartments, generally 

 usual character, the other being triradiate relied upon, we con.^ider unessential, and 



