Art. III. — Groivth stages in modern Ti-igonias, belonging 

 to the section Pectinatae. 



By T. S. hall, M.A. 



[Eead 13th June, 1901]. 



The molluscan genus Trigonia Bruguiere, has been divided into 

 a series of sections which, though well marked, yet merge into 

 one another so that Lycett considered it inadvisable to erect 

 them into genera or even sub-genera.^ The living Australian 

 species, he says, are a gi^oup apart, and to the section formed by 

 them the name Pectinatae or Pectinidae has been applied. Lycett 

 refers T. subundulata, Jenkins ( = T. semiundulata, McCoy), to 

 the same group. The resemblance of this fossil form to the 

 members of the section Costatae had previously been called 

 attention to, but Lycett points out that it differs from that 

 group in that its valves are equal and similar in ornament, 

 whereas in the Costatae a separate description for the two valves 

 is required. It would then appear justifiable to refer all our 

 modern Australian Trigonias to the same group. 



The question of the discrimination of our recent species is one 

 of difficulty, for considerable variation is shown both in the 

 shape of the shells and in their ornament, and, probably, the 

 last has not been heard on the question. Four species seem to 

 be generally accepted — T. strangei, T. lamarckii, T. margaritacea, 

 and T. viniophora. To these McCoy added T. acuticostata which 

 he originally described as a fossil, and Tenison Woods described a 

 vai'iety of T. lamarckii to which he applied the name reticulata.- 

 Whether this variety is distinct from McCoy's acuticostata and 

 whether that is or is not a variety of a living species I am not 

 prepared to say. 



The species from our tertiary beds are : T. subundulata, Jenkins ; 

 T. intersitans, Tate ( = T. tatei, Pritchard) ; T. tubulifera, Tate ; 



1 Palgeontographical Society, 1872. 



2 Proc. Linn. Soc. N. S. Wales, vol. ii., 1S77, p. 125. 



