TERATOLOGY OF DIATOMS. 6l 



a second medium nodule appears, with stria; radiating from it in all 

 directions. 



22. Biddulphia balcena, Ehr. = Triceratium formosum, BrighlweV. 

 Spitzbergen, Arctic Sea ; recent. A large Biddulphia form, in which 

 the delicate marking radiates from four or more distinct points as 

 centres. 



Ill Marking unsymmetrically varied. 



23. Coscinodiscus robustus, Gnv. Pabellon de Pica, S.A. ; guano. 

 The areolation is so irregular as to have lost all hexagonal form. Its 

 strong margin, robust habit, and its occurrence among typical specimens 

 of similar size, etc., fix the specific relation. A similar example in 

 same species was found in the Santa Monica deposit. 



24. Arachnoidiscus Ehrenbergii, Bailey. Santa Monica, Cal. ; fossil. 

 The radiating costae, irregularly wavy, and anastomosing near the 

 centre, where they also become fainter and hardly traceable. 



25. Adinoptychus Heliopelta, Grun. Nottingham, Maryland ; fossil. A 

 specimen with five elevated rays. These are plainly distinguished at 

 the central zone, but the undulations flatten out soon, and the outer 

 part of the shell is quite flat and evenly areolated. The rim, with 

 its irregularly scattered spines, is typical. 



26. Triceratium affine, Grun. Samoa Islands, Pacific Ocean ; recent. 

 The areolation is so irregular as to lose entirely its hexagonal character ; 

 this is the case all over the shell. Its size and outline, and its 

 occurrence among numerous typical specimens show its relations. A 

 second example has been noted on another slide from same locality. 



27. Amphitetras antediluviana , Ehr. Kiel, Baltic Sea ; recent. The 

 central part of the shell is irregularly areolate, with a tendency to two 

 centres. The typical forms, common in same gathering, have the 

 central areolation evenly concentric. 



28. Naviada elliptica, Kg. Crane Pond, Mass ; recent.' The striation 

 is irregularly wavy, especially at the ends. 



29. E/if hernia turgida, Kg. Berlin, Germany ; fossil. The costs? and 

 areolation are so irregular as to destroy all pattern in one-half the 

 shell and nearly so in the other. 



30. Nitzschia scalaris Ehr. Sodertelge, Sweden ; recent. In one part 

 of the shell the keel is distorted, and instead of it appear two nodules 

 on the face of the shell with irregularly radiating striae. 



" Whenever I speak of striation I mean to be understood that it is 

 resolvable into dots, similar in character to those of the typical forms 

 of same species, 



