112 CRETACEOUS PELECYPODA 



B. Tellinacea with a strong external ligament, but without a cartilage in the 

 hinge. 



XI. Family— TELLINIDu^. 

 (TELUNiNJE, H. and A. Adams, Tellinid^e and PsAMMOBiWAi of Deshayes/ 

 Animal with a strongly compressed lingui-form foot, the siphons long and 

 wholly separated, the inhalant shorter, but more muscular and thicker than the 

 exhalant ; the palpi variable in size, but usually large and coarsely striated ; gener- 

 ally with two unequal gills on each side of the body, sometimes distinct only near the 

 posterior ends, where they are united, narrow, but usually much longer than the 

 palpi. The shells are transversally elongated, posteriorly more or less attenuated, 

 or truncated, gaping behind and sometimes also in front, thin, entire at the mar- 

 o-ins ; beaks small, not very prominent ; hinge composed of one or two cardinal 

 teeth, lateral teeth present or wanting ; ligament external on more or less promi- 

 nent or thickened fulcra ; pallial sinus deep and often very large. 



The Tellens are among the oldest known shells, but the diiferent forms Avhich 

 they present have been variously classified by conchologists. Lattreille first 

 grouped most of them, then known, under a special family name, Tellinibm ; but 

 many subsequent changes and corrections have been made by several of our best 

 conchologists. 



I have already mentioned the classification of H. and A. Adams in their 

 admirable work, the Genera of recent Mollusca. They place our shells as a sub- 

 family beside the DOSACiNJE, scsosiculariiNjE, tmd PAPEiiNM. Dcsliaycs was the 

 first to draw attention to the differences which exist between the animals of 

 the group of Gari (his Fsammobiibm) and those of other Tellwidm; but I 

 think that author's separation of the shells into two families is neither necessary 

 nor fully justified by any very essential differences. Deshayes rightly says that 

 the shells do not offer any particular distinctions, at least not such as 

 would entitle them to rank as two distinct families, but he says that the animals 

 of the QARiNM possess small palps and two gills on each side, while all the 

 TELLiNiNM havc large palps and only one gUl on each side. This would no 

 doubt be thought of importance, for this fact being sufficiently well established, 

 there "■enerally could be some distinctions pointed out in the shells which 

 would assist in the separation. But I am afraid that the character specified 

 reo-arding the number of gills is not a general one in tellwism, and I do not 

 even know whether it holds good at all. I have examined the animals of 

 Tell, rugosa, rosea, and a few others, and found that the gills are in those species 

 always long and narrow, the two plumes are grown together in front, but more or 

 less distinctly separated posteriorly, where the gills from both sides join each other ; 

 however, even at the anterior part where they certainly appear as a single gill, the 

 median furrow separating the two plumes can be traced without much difficulty. 

 I hope to be able to return to this anatomical question at the earliest oppor- 

 tunity. 



