274 Sir N". Yermoloif — Diatom Earth in California. 



are so scarce that their presence may perhaps be considered as 

 accidental. Thus there are no Arachnoidisci, so common in warmer 

 waters and present even in the Los Angeles deposit ; only one 

 Coscinodiscus 'pateUceformis Grev. has been found, and no 

 Craspedodisci have occurred. Only very few specimens of Cos- 

 cinodiscus bulliens A. S. and C. turgidus Rattr., which are truly 

 southern forms, have been observed. There are in Lompoc, it is 

 true, many forms belonging to the group of Coscinodiscus marginatus 

 Ehr., but the marginatus group can hardly be considered as strictly 

 southern, this group being often met with, as in the Mediterranean 

 Sea. On the other hand, Lompoc has very few representatives of the 

 genus Ste])hanopyxis, or even of Melosira, species of which are 

 common in warm waters. The genus Actinocyclus is entirely absent ; 

 on the other hand, one Actinocycloid form, namely Euodia gibha 

 Bail., is not only abundant in Lompoc, but even dominating, just 

 as it is equally frequent in the Moron deposit of Spain. The 

 Actinoptyclius forms in Lompoc are very poor ; there are many 

 specimens of A. undulatus Ehr., but they are nearly all of extremely 

 small size, not exceeding some 30 microns. The genus Asterolampra 

 is represented by two species, A. Grevillei Wallisch. and A. rotula 

 Grev., both very frequent, just as they are frequent in the 

 Mediterranean. The genus AsteromjjJialus is also represented by 

 two species, A. Moronensis Rattr., common in the Moron deposit, 

 and A. Hookeri Ehr., frequent in the Antarctic. 



Together with Dictyocha and Euodia, the genus Coscinodiscus- 

 dominates in Lompoc. Indeed, these three genera share between 

 them nearly the whole number of organisms in Lompoc. 



Of the nine groups of the genus Coscinodiscus, as tabulated by 

 Rattray, in his " Revision ", only five groups are represented in 

 Lompoc. These five groups are the Inordinati, the Excentrici, the 

 Lineati, the Fasciculati, and the Radiati. The four others, the 

 Cestodiscoidales, the Eleganti, the Elaborati, and the Cocconeiformes, 

 are absent. 



Of the five groups present, the dominating one is that of the 

 Radiati. This is made evident by the following statement of the 

 respective numbers of species : Inordinati, 1 species ; Excentrici, 

 3 species ; Lineati, 8 species ; Fasciculati, 1 3 species ; Radiati, 

 25 species ; total, 50 species. Besides these fifty species there are 

 in Lompoc many intermediate transitional forms between the 

 Excentrici and the Lineati, but their occurrence is not remarkable, 

 because such transitional series are also observable in European 

 seas. 



A curious fact concerning the Fasciculati group is the following r 

 Coscinodiscus suhtilis Ehr. so common in European seas, is 

 poorly represented in Lompoc by very few and small specimens ; 

 also, no so-called " derivatives " of C. suhtilis, such as C. Kutzingii 

 A. S., C. Normani Greg., and C. Rothii Grun., are to be found. 

 It would appear as if the stibtilis group had had no good opportunity 



