JUKES-BEOWNE : ON CALLISTA, AMIASTIS, AXD PITARIA. 339 



in some specimens it is either absent or -was so slight as to have been 

 broken and detached ; the same is the case with the West Indian 

 fuhninata (Menke). There is, in fact, every gradation between 

 a complete arch and an incomplete one, proving that the character 

 is of little value as a basis of generic or sub-generic distinction. 



Dr. Dall based his Agriopoma group on three characters: (1) 

 a continuous cardinal arch in the right valve, (2) a chalky shell 

 without coloration, (3) an angular pallial sinus; and he placed it as 

 a sub-genus of Calloeardia, taking Texasiana, Dall, as the type and 

 excluding P. fuhninata. It is clear, therefore, that his small group 

 of American shells is not the large group which I distinguish by 

 another set of characters, and for which I now propose the name 

 Pitarma, indicating P. citrina as the type. This I regard as a section 

 of Pitaria, distinguished by a free oblique posterior cardinal in the 

 right valve and a short pallial sinus ; the valves are frequently 

 coloured with brown markings, and there is often a complete cardinal 

 arch in the right valve. 



So far as I can ascertain, there are only five other reputed species of 

 Pitaria which agree with the type. One of these is P. cor, Romer 

 {non Hanley), which only differs from tumens in being more trigonal 

 in shape, and may be regarded as a mere variety ; another is 

 P. rnfescens, which seems only to differ in colour, but is said to come 

 from the Philippine Islands, while tumens is a native of West Africa. 

 The third is P. virgo, which also comes from West Africa and differs 

 very little from tumens, but in which the posterior cardinal is not 

 quite so completely confluent with the nymph. The other two 

 species are P. manillce, Sow., and P. tumida, Sow., both of which are 

 trigonal and concentrically ribbed. It is therefore these five species 

 or varieties which, with P. tumens, will form Pitaria, se7isu stricto. 

 The true Cytherea cor (Hanley) is a very different shell from that 

 above-mentioned. 



We cannot leave the Pitaria group without taking notice of the 

 shell described by A. Adams under the name of Callocardia, and of 

 certain other shells which have been associated with it. Callocardia 

 was founded in 1864 on a single left valve, and Adams thought that 

 it did not possess an anterior lateral tooth, for he distinctly wrote 

 "dentibus lateralibus nullis ".^ In 1883 (Challenger Reports, 

 MoUusca) Mr. E. A. Smith doubtfully referred three new species 

 of shells to Callocardia, but in the following year Dr. Dall proposed 

 the genus Vesicomya for these and another new form ( V. venusta, 

 Dall).- In 1888 Mr. G. B. Sowerby, having obtained perfect 

 examples of the original species Callocardia guttata, pointed out 

 that its dentition agreed more closely with that of Caryatis than 

 Avith that of Miocardia, near which it had been placed by Adams. 

 In 1900 Mr. Smith confirmed Sowerby's view,^ and figured the 

 hinges of both valves of C. guttata; indeed, he went farther and 



' Ann. Mag. Nat. Hist., vol. xiii, p. 307, 1864. 

 - Bull. Mus. Comp. Zool., vol. xii, p. 272. 

 ' Proc. Malac. Soc, vol. iv, p. 81. 



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