JDKES-BKOWNE : SYNOPSIS OF THE TENERID^. 89 



The genus Tapes. 



Even after the separation of Marcia and its allies, the shells which, 

 have been grouped under the head of Tapes form a heterogenous 

 assemblage which is difficult to define in terms that would be 

 applicable to all of them. If we neglect the variations in shape 

 and external sculpture, and confine our attention to the internal 

 characters, we find that the group typified by Tapes litteratus differs 

 considerably from that which was called Textrix by Homer, and still 

 more from the shell which is commonly known as Tapes pullastra, 

 which last is in many respects more closely allied to Venerupis than 

 to Tapes proper. So great is this resemblance that the cavicolar 

 variety of T. pullastra was supposed to be a distinct species by 

 Lamarck, and was by him classed as a Venerupis under the name of 

 V.perforans. 



After a careful examination of the two assemblages which have 

 gone under the names of 2\ipes and Venerupis I have come to the 

 conclusion that they really form a connected series with 'Tapes 

 litteratus at one end and Venerupis irus at the other ; and further 

 tliat it is almost impossible to frame a definition of the one that 

 would exclude the other. Consequently I would either make one 

 genus of them under the name of lapes with Venerupis as a sub-genus, 

 or divide the series into three genera which could then be more easily 

 defined and distinguished. On the whole, and having special regard 

 to the characters of the hinge, I prefer the latter arrangement, and 

 find it more convenient to create a new genus for the shells which 

 occupy an intermediate position between the two extremes. 



Here, however, we are brought up against the thorny fence of 

 priority iu the selection of a name and type for this intermediate 

 genus. The groups of which it can be formed are those for which 

 the following names have been proposed : Textrix, Paratapes, Pullastra, 

 Polititapes, Callistotapes, and Prota2}es. Of these, Pullastra is the 

 oldest, having been proposed by Sowerby in 1826, while the Textrix 

 of Komer only dates from 1857, and was, moreover, preoccupied by 

 Sundeval in 1833, so that the next name was Paratapes (Stoliczka, 

 1871). Pullastra, however, can only be recognized as a subsidiary 

 group, whereas the type of Paratapes is the first species on Eomer's 

 list of Textrix, so that the one name could stand for the other, and 

 could be defined so as to include the same species. 



Under the International Rules, however, tlie oldest name in any 

 assemblage of groups must be taken as the generic name, and, if we 

 submit to this ruling, Pullastra would be the name of the genus, and 

 Paratapes would have to rank as a sub-genus. The only other way 

 out of the difficulty is to detach Pullastra from the intermediate 

 genus, and to consider it as a sub-genus of Venerupis. This indeed 

 I regard as the most convenient and most natural arrangement of the 

 several groups, for Pullastra is intimately connected with Venerupis 

 through the species which were separated by the Messrs. Adams 

 under the name of Jfi/rsus. Some of these species have since been 

 referred to Tapes and some to Venerupis by different authors, but 

 they are best united under the head of Pullastra. 



