JUKES-BKOWNE : SYNOPSIS OF THE TENEEID^. 77 



groups Cliione^ Anoynalocardia, and Clausinella as sub-genera of 

 a comprehensive genus Venus. 



With regard to Timodea, of which the type is Ve7ius ovata, Pennant, 

 I am convinced that it cannot be separated from the typical section 

 of Chione either solely or principally on the ground of its external 

 sculpture. There is every gradation between the cancellated forms 

 of Chione and the Timodea type, in which the concentric ridges are 

 reduced to scales or nodes on the radial ribs. The distinction must 

 be found in other points of difference, and Venus ovata can be grouped 

 with other species which have a similar ovate sub-equilateral shape, 

 the same widely divergent teeth, with an obtuse or rounded pallial 

 sinus ; I also find that in all these species the pedal scars are separate 

 from those of the adductors, while in the typical section of Chione 

 there is almost always an open connexion between the two scars, 

 which means of course a more or less complete union of the pedal and 

 adductor muscles. 



In this connexion it is curious to find that M. Cossmann has 

 proposed to make Timodea a separate genus, but this estimate of its 

 importance is partly due to his confusion of Chione with Antigona. 

 Moreover, he relies entirely on the characters of T. ovata, and con- 

 sequently he does not give such a comprehensive definition of Timodea 

 as would make it comprise such species as V. marica, V. striatissima, 

 V. suhnodulosa, and V. arakanensis. It may bo noted also that the 

 straight inner border of the hinge-plate, which he mentions as 

 distinctive, is largely a function of the sub-equilateral shape of the 

 shell, for an oblique curvature of the shell naturally produces 

 a curvature of the hinge-line. 



Again, the differences between the Clausinella of Gray and the 

 Lirophora of Conrad (which should have been written Lirifera) seem 

 to me so small and unimportant that no good purpose can be served 

 by laying much stress on them. The real fact is that these names, 

 through the types attached to them, belong to exceptional forms of 

 a large natural group. Thus Venus fasciata is a European form, 

 which, in its compressed shape and its sculpture of broad flattened 

 ridges, stands quite by itself, while Conrad's type was a fossil nearly 

 allied to the West Indian Venus paphia, Linn., a species in which the 

 ridges pass into erect posterior expansions, and also exhibit an obscure 

 radial striation. 



Now the natural group to which these species belong is that 

 typified by Venus tiara, Dillwyn, V. herryi. Gray, and V. rohorata, 

 Hanley. It was this group for which Miirch, in 1853, used Klein's 

 name of Circomphalus, and if subsequent writers had only taken note 

 of this (Tryon, Sacco, and Dall) tliey would not have chosen V. jiUcata 

 as the type (see ante, p. 73). The name Clatisinella, however, was 

 published in 1851, and has priority, so that obviously the best course 

 to pursue is to adopt it for the whole natural group, though Lirophora 

 may be used for the few recent American shells which conform to 

 Dr. Dall's definition, and for their fossil representatives. 



Venus gallina, the type of Morch's Chamelea, is another exceptional 

 form which is allied to the V. tiara group, and seems to be connected 



