OF SOUTHERN INDIA. 1C3 



III. Order. TELLINACEA. 



[Telu.md.e apud H. and A. Adams). 



Looking at the large number of the so-called Tellina-QYO\i\) of shells there are 

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

 order of the Pelecvpoda. The animals all possess entirely divided siphons of oreat 

 length, the mantle is only partially imited 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 jiosteriorlv 

 above the siphons ; the two leafletts composing the gills on either side of the body 

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

 of the TELLINACEA are always considered as particularly elegant in form and 

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

 more or less elongated, posteriorly generally flexuous, a more or less distinct ridge, 

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

 posterior end. The surface is usually ornamented with very regular concentric 

 striae or ribs, and if any other ornamentation appears, it always shows a great regu- 

 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 

 j)resent. The pallial sinus is with few exceptions large ; the ligament is generally 

 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, Tellinibm, 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 

 f<n'mer belong the Paphiid^ f= Mesodesmid^J and Scrobiculai{iid.e (^ Ampei- 

 desuibm) ; to the latter the Tellinidje and Donacib^. The reason for uuitino- 

 Deshayes' Tellinid^ and Psammobiid^ f= Oarix.bJ will be detailed subsequently. 

 Among these four families, as here accepted, the Papriidm and Dosacid.e on the 

 one side and the Scrobiculasiid^ and Tellinid^ on the other may be said to form 

 imrallel divisions ; each two, respectively, exhibiting in form and in the solid or thiu 

 structure of their shells very marked relations. As the shells with an internal ho'a- 

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

 begin with the family Paphiid^e, especially also because they very much recall some of 

 the characters of the Mactrid.e, though, as already stated, the oarin.e and other 

 Tellinidm offer the greatest resemblance to the prarellinm of the SoLENivji. 



