Sir JSf. Yermoloff — Diatom Earth in California. 275 



to evolve in Lompoc. On the other hand, another branch of this 

 same group, the odontodiscus branch, developed well and safely 

 along two other branch-lines, the odontophorus branch and the 

 interlmeatus branch . 



It is remarkable that in the Excentrici group Lompoc possesses 

 the species known under the name of Coscinodiscus decipiens 

 Grun., common in the Baltic. 



We now turn to the analysis of the dominating Radiati group. 

 Its radiatus subgroup, with its derivative Coscinodiscus Argus 

 Ehr., is very numerous. The oculis-iridis subgroup is also very 

 numerous with its large-sized derivative, Coscinodiscus borealis Bail. 

 Coscinodiscus centralis Ehr. is also numerous, but, curiously enough, 

 the closely allied C. concinnus W. Sm. and C. nobilis Grun., common 

 in the Baltic and the Mediterranean, are totally absent. 



The marginatus subgroup with its numerous derivatives, as shown 

 in the appended list, is fairly numerous, though, as has been stated, 

 this subgroup is already more or less transitional to southern forms. 

 There are two interesting facts to note in its occurrence at Lompoc : 

 in the first place there are many specimens of the so-called C. 

 robustus, with exterior "springs" as described on p. 64 of Rattray's 

 "Revision", and peculiar to the Californian Santa Monica deposit. 

 In the second place there are some Coscinodiscus forms closely 

 resembling tests of Pxyidicida, a genus sometimes considered to 

 belong to the Rhizoj)ods. 



These forms have convex valves with punctuate alveoles. The 

 punctae on the alveoles are very clear and conspicuous. It is just 

 possible that the forms mentioned in the appended list as C. bipartitus 

 Rattr., or C. blandusA. S. may be tests of Pyxidicidce, also perhaps 

 C. robustus Ya,i\ fragilis Rattr. The specimens from Lompoc classified 

 as C. bipartitus are quite similar to the figures given by Professor 

 De Toni in his work, Ancdisi microscopica di alcuni saggi di fitoplankton 

 raccolti dalla R.N. Liguria, but they have no lobes, a circumstance 

 hardly to be considered as unexpected, these lobes being of a non- 

 siliceous composition and therefore not able to withstand the effects 

 of fossilization. On the other hand, some of the forms in question 

 rather resemble Pyxid.icida Mediterranea Grun., a form not 

 unfrequent in the Mediterranean Sea. The whole question is, 

 however, as yet a subject of controversy requiring further elucidation. 



A very curious fact in the Fasciculati group is exhibited in Lompoc 

 in connexion with the species, C. curvatulus Ehr., C. radiolatus 

 Ehr., C. radiosus Grun., C. ceginensis A. S., and C. nodidifer Jan. 

 All these sj)ecies show something like a distinct nodule, whilst 

 their fasciculate structures are extremely alike, the species passing 

 from one to the other by most insensible gradations. 



The genera DictyocJia, Euodia, Coscinodiscus, and Thalassionema 

 dominate, and give to the deposit its characteristic facies. It has 

 undoubtedly a much more northern facies than, say, the deposit 

 from Los Angeles, which contains many more southern forms. 



