82 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



Genus HERCOTHECA Ehrenberg 



The strong suspicion that the forms composing this genus are only 

 endocysts escaped from frustules of Rhizosolenia or kindred general 

 has resulted in its general abandonment; and it is included here with 

 no actual belief in its validity, but because as yet these bodies are 

 impossible to definitely assign elsewhere. Whether endocysts or not, 

 they represent certain species of diatoms that exist in the flora in 

 which they occur, and should therefore be so included until a better 

 assignment can be made. 



HERCOTHECA INERMIS, new species 



Plate 18, figs. 1-2 



Front views of the two valves dissimilar; both circular, both hav- 

 ing the entire surface closely wrinkled into a strong network of 

 anastomosing lines, both with an inner concentric circle and a small 

 central dot or knob; but the inner circle of one valve obscure and 

 near the margin, of the other distinct and midway between the mar- 

 gin and the center; the side (girdle) view explains the difference, one 

 valve being almost evenly hemispherical or dome-shaped, with a slight 

 undulation in the curve near the margin; the other having its hemi- 

 spherical contour compressed to an almost conical elevation, the 

 basal width of which is one-half that of the valve ; girdle narrow, thin, 

 and hyaline. 



Diameter, 0.062-0.073; width of frustule, 0.053-0.059 mm. 



Although this species shows no trace of the circle of spearlike spines 

 which arise vertically from each valve of the uncommon genus Herco- 

 theca in each of its two known species, H. mammillaris Ehrenberg 

 (Mikrogeologie, pi. 33, sec. 18, fig. 7; Pritchard, Inf., pi. 7, fig. 35) 

 and H. brevispina Grunow (Cleve and Moll, Diat., No. 215) it differs 

 in no other essential respect. In fact the side views are otherwise 

 identical, and the chief characteristic, the dissimilarity of the two 

 valves, is quite pronounced. Therefore, although a new genus was 

 planned to receive this unique form, the interests of taxonomy seem 

 to be better met by assigning it to Ilercotheca. 



As mentioned above, the assumption may be made that it is an 

 ornate and unusually large example of endocyst of some cylindrical 

 diatom, like Rhizosolenia; and there is a possibility that future research 

 may prove it to be so. But although this form is frequent in several 

 Philippine Islands dredgings and the dominant object in one of them, 

 I have not been able to find a trace of any diatom to which it can be 

 referred. If one were to suppose that the investing diatom was 

 so delicate and pellucid as to escape detection in examinations of 

 the uncleaned material and to be entirely obliterated by the acid 

 process of cleaning, the classification of this form as an endocyst 

 would be possible. But after much consideration, the above assign- 



