172 BULLETIN" 100, UNITED STATES NATIONAL MUSEUM 



Genus TRINACRIA Heiberg 



The species classified under this name are generally recognized to 

 be merely triangular phases of the genus Hemiaulus (Ehrenberg) Gru- 

 now. They are principally found in fossil deposits, notably those at 

 Mors, Denmark, and Simbirsk, Russia. A coarse, blotchy style of 

 marking and stiff, straight processes tipped with stout spines that 

 rise vertically from the angles of the valves are equally characteristic 

 of both, the processes being two on the biangular Hemiaulus and three 

 on the triangular Trinacria. Van Heurck makes this essential unity 

 clear by figures in Van Heurck's Treatise, page 456. He there also 

 adds to Hemiaulus a quadrate phase for which Heiberg created the 

 genus Solium and an unsymmetrical biangular phase for which 

 Heiberg created the genus Corinna. How that diatomist could sep- 

 arate generically such evident examples of Hemiaulus as the last is 

 a mystery. 



But Trinacria has at least one quality that is favorable to its reten- 

 tion as a convenient division of diatom taxonomy — the fact that 

 these triangular forms are very rarely or never anything but triangu- 

 lar; that is to say, do not vary into the typical biangular Hemiaulus 

 phase, and can therefore never be confused with strict Hemiaulus 

 species. In the superficially similar genus, Trigonium, and especially 

 in the old conglomerate Triceratium, two, three, four, five, or more 

 angled modifications of the type form are common. But the persist- 

 ent triangular shape maintained by the 30 or more species of Trina- 

 cria makes their retention in a group a material help in identification. 

 I therefore retain this generic name, subject to the foregoing statement 

 of agreement with H. L. Smith, Grunow, Van Heurck, and other dia- 

 tomists, who have carefully considered this subject. 



TRINACRIA LIMPIDA, new species 



Plate 39, fig. 1 



This species resembles rather closely two examples of T. wittii A. 

 Schmidt figured in Schmidt's Atlas, plate 96, figure 1, and plate 97, 

 figure 2, and the phase of the same thing accepted as such by Schmidt 

 and figured in Witt's Diatoms of Simbirsk, plate 11, figure 1. But 

 the Philippine specimens have undulating sides, delicate lines radi- 

 ating from a central rosette, on which are strung widely separated 

 beads, as on threads; a strongly contrasting single row of large, oval 

 beads along the margin, and with decidedly rounded apices marked 

 with minute, closely set beading arranged fan wise; in all of which it 

 contrasts with T. wittii, especially with the latter's produced and 

 apiculate apices. In fact, there is less doubt of the separateness of 

 these two than the wisdom of calling either of them anything more 

 than wide varieties of T. regina Heiberg. 



Diameter of valve, from apex to middle of opposite side, 0.107 mm. 



Type— Cut. No. 43695, U.S.N.M. 



