335 



ON CALLISTA, AMIANTIS, AND PITARIA. 

 By A. J. Jukes-Browne, F.R.S., F.G.S. 



Bead 9th Mmj, 1913. 



The large group of shells which was called Callista by Morch (1853) 

 ami by the Adams Bros. (1857), and Dione by Gray (1847), was 

 divided by Homer iuto three sections (1857 and 1862), which were 

 really genera, for he regarded them as co-ordinate with Tivela, 

 Meretrix, and Circe} His divisions were Callista for the Venus chione 

 group, Caryatis for the C. tiiinens group, which he had called Fitar 

 in 1847, and Dione, which he restricted to the Venus dione group, 

 but included D. nohilis, which is the Cytherea callosa of Conrad, and 

 for which Carpenter proposed the sub-genus Amiantis. 



A little later (1876) the whole group was briefly reviewed by 

 Meek, who thought all these divisions might be reunited into one 

 genus under the name Callista (Poll & Adams). Of this genus he 

 made six sections or sub-genera, including Homer's three groups, and 

 adding to them a sub-genus Macrocallista, and the fossils Aphrodina 

 (Conrad) and Dositiiopsis (Conrad). 



More recently (1902) Dr. Dall published a "Synopsis of the 

 Veneridse",- in which he regarded most of these groups as separate 

 genera, discarded the name Callista, and made a still further sub- 

 division of them so that his genera and sub-genera are as follows: — 



1. Macrocallista, Meek, with sub-genus Chionella, Cossmann. 



2. Amiantis, Carpenter, with section JEucallista, Dall. 



3. Callocardia, Adams, with sub-genus Af/riopoma, Dall. 



4. Pitaria, Homer, em., with sub-genus Hysteroconcha. 



5. Aphrodina (as sub-genus of his Cytherea, Bolten). 



A comparison of this arrangement with those of Rdmer and Meek 

 has convinced me that Homer's is much more natural and satisfactory 

 than either of the others. I propose to give my reasons for this 

 opinion and to bring under review some other small groups of shells 

 which are closely allied, viz. the Tivelina of Cossmann, the Lepidocardia 

 and Transenella of Dall, and that for which 1 proposed the name of 

 Calpitaria in 1908. 



If it be argued that all these groups are so closely allied that 

 they form no more than one genus, there is little fault to be found 

 with Meek's arrangement, for we need then only exclude Dosiniopsis, 

 which indeed he included with some doubt. It may be admitted 

 that the groups above mentioned are linked together by species which 

 combine the characters of two or more of them. At the same time 

 there is no reason why we should not accept the existence of links 

 between groups which it is otherwise convenient to regard as separate 

 genera. 



^ Krit. Untersuchung der Arten des Moll. Venus, Cassel, 1857; and Malakozool. 



Blatter, Bd. viii, 1862. 

 ^ Proc. U.S. Nat. Mus., vol. xxvi, p. 335, 1902. 



