49 6 



ACTINOPTYCHUS. 



Symbolophora Ehr., 1844 (non Grunow), with valves having an 

 angular centre. 



Heliopelta Ehr., 1854, the type-form of which is A. Heliopelta 

 Grunow (fig. 235), characterised by its numerous spines or teeth on the 



margin. 



Halionyx Ehr., 1854, includes such of the Actinoptychus as have the 

 central portion rounded. 



Polymyxus Bail, 1885. are the Actinoptychus without a cellular layer, 

 and with strongly undulated valves. In the text (fig. 236), will be found 

 Polymyxus pulchellus, Gr., which deviates somewhat from the normal type- 

 form (P. toronalis L. IV. Bail.). A figure of the latter will be found in H.V.H. 

 Atl., pi. 123, f. 4, which is identical with an Actinoptychus, where the cellular 

 layer is absent. 



Schuettia De Toni, 1894, are Actinoptychus with triangular valves ; 

 the figure in the text (fig. 237), represents A. annulatus ( Wall.) Grun., which 

 is the type-form of this new genus. This form is met with at Java and in the 

 China Sea. If a new genus is to be constituted for triangular forms, the name 

 given by Dr. De Toni is untenable, but it should be called Cymatogonia, 

 which was proposed by Mr. Grunow in 1883, in the "Botanisches Centralblatt," 

 No. 36 (vol. xv., No. ro). 



There are only two Actinoptychus to be found in our regions. 



ANALYSIS OF SPECIES. 



"Valve having usually six compartments, with large hexagonal central 



umbilicus . . . . . . .A. undulatus. 



- 



Valve having from 12 to 20 compartments, with umbilicus dentate, teeth 

 ,. truncate ... . . A. splendens. 



A. undulatus Ehr. (Act. Mternarius Ehr., Mik., pi. 18, f. 20; 

 H.V.H. Atl., pi. 122, f. 1 and 3, and pi. 22 bis, f. 14* ; Type N0.514), plate 

 22, fig. 648. 



Valve usually with six compartments, a large umbilicus, polygonal," central, 

 smooth, and usually furnished with a small process, placed on the submarginal 

 median portion of each alternate compartment. Alveolate lamina, with large 

 hexagonal alveoli; punctate lamina, with puncta fine, in quincunx; about 16 

 striae in 1 c.d.m. Diameter of valve, about 4 to 12 c.d.m. 



Marine. Common. Blankenberghe, Ostend, Antwerp (Scheldt.), and in all mud deposits of the 

 North Sea. England (W, Sm., Hodgson, Kilton, Stolt,, Norman, Comber), London clay 

 (Baxter Coll., No. 2309), Northumberland (Baxter Coll., No. 2829), Devonshire (Baxter Coll., 

 No. 2841), 



