OE SOUTHEEN INDIA. 103 



III. Order. TELLINACEA. 



{Tellinidje apud H. and A. Adams). 



Looking at the large number of the so-called TelUna-^vowp of shells there are 

 some distinctive peculiarities traceable which entitle them to be classed as a separate 

 order of the Eelecypoda. The animals all possess entirely divided siphons of great 

 length, the mantle is only partially united below and widely open in front, the 

 foot large, compressed, and lingui-form at the end ; the palpi are large and trian- 

 gular, usually coarsely striated ; the gills narrow, long, partially united posteriorly 

 above the siphons ; the two leafietts composing the gills on either side of the bodv 

 are generally unequal, and one of them is sometimes nearly obsolete. The shells 

 of the T]]]LLINACJEA are always considered as particularly elegant in form and 

 ornamentation ; they are usually strongly compressed, thin or solid, transversally 

 more or less elongated, posteriorly generally flexuous, a more or less distinct rido'e 

 or plicature, running from the beaks along the postero-superior margin to the 

 posterior end. The surface is usually ornamented with very re^^ular concentric 

 strige or ribs, and if any other ornamentation appears, it always shows a great reo'u- 

 larity, and this character especially is it which gives the shells their elegant appear- 

 ance. The hinge is, as a rule, composed of two cardinal teeth in each valve, 

 occasionally one of them in one or the other valve becomes obsolete, but verv 

 rarely is there an additional cardinal tooth in one valve ; lateral teeth are often 

 present. The pallia! sinus is with few exceptions large ; the ligament is generallv 

 strong and distinct, rarely nearly obsolete; a cartilage appears occasionally, but 

 does not form one of the essential characters of the shells. H. and A. Adams have 

 classed the whole of this order in one family, Tellinib^, but there can be little 

 doubt that the peculiarities which many of the shells exhibit make it very desirable 

 to distinguish several families, as has been many years ago suggested by Deshayes. 

 Only when such divisions are fairly established will it be possible to make a 

 proper comparison between the various forms of the TELLINACEA and the 

 VENERACEA. 



With regard to this point of classification two principal divisions, or tribes, can 

 first be traced out : some with an internal cartilage and others without it. To the 

 former belong the Papriid^ f= Mesodesmid^J and Scrobiculariibm f= Amphi^ 

 desmijdm) ; to the latter the Tellinib^ and Donacibm. The reason for uniting 

 Deshayes' Tellinibm and Fsammobiib.e f= Oauinm) will be detailed subsequently. 

 Among these four families, as here accepted, the Faphiib^ and Donacibje on the 

 one side and the Scbobiculapiibm and Tellinibm on the other may be said to form 

 parallel divisions ; each two, respectively, exhibiting in form and in the solid or thin 

 structure of their shells very marked relations. As the shells with an internal liga- 

 ment are often considered to be more highly organised than those without it, I shall 

 begin with the family Fapeiibje, especially also because they very much recall some of 

 the characters of the Mactrib^, though, as already stated, the qarinm and other 

 Tellinibm offer the greatest resemblance to the pharellinje of the Solenibj^l 



