90 CEETACEOUS PELEOYPODA 



The shells are inform intermediate between the Saxicavid^ and the Solunid^; 

 they are elongated, inequilateral, occasionally slightly nacreous inside, with the 

 pallial impression sometimes partially interrupted, or undulating, and with the 

 pallial sinus deep. The hinge has numerous teeth in each valve ; there is a very thin 

 cartilage substance present, situated above the posterior laminar teeth, and besides 

 a strong ligament externally above it, partially covering the same and somewhat 

 internally attached behind it posteriorly. H. and A. Adams place this family in 

 the TUNER A CUA next to the Fetricolid^, which can scarcely be admitted as 

 correct. The animals of both Glauconomya and Tanysiphon which I have examined 

 are, as I stated, externally much like those of Mya or Anatina, while in the 

 Petricolid^ we find two short sub-equal siphons separated for the greater part of 

 their length, and not covered with the epidermis of the shell, which in the 

 Glauconomyidm forms a regular tube over the siphons. These are, however, fully 

 retractile within the shell, as we find them in the Solbnidm, Mactbidm, and some 

 species of the Anatinid^, while in other allied forms, like Anatina or Cyrtodaria, 

 the siphons are not perfectly retractile. 



The only resemblance existing between the Glavconomyibm and Fetricolibm 

 lies in the dentition of the hinge, not in the structure of the shells, which are 

 thin and somewhat pearly in the former, thick and solid in the latter. The anterior 

 hinge-teeth are in both no doubt similar, but they do not, on the other hand, difi'er 

 essentially from the hinge-teeth of Novaculina. In the Fetricolid^ the single one 

 or two posterior teeth fit closely beside each other, exactly as do the anteriors when 

 the valves are closed ; but in the Glauconomyid^, the posterior teeth are bifid, their 

 smaller portions fitting one above the other, and the hinder larger portions possess 

 flat surfaces for the attachment of a thin white cartilage. This last is very distinct 

 in Tanysiphon, in which the ligament is small, but in Glauconomya, in which the 

 cartilage becomes sometimes quite obsolete, the ligament predominates. For this 

 reason I do not wish to lay too much stress upon the presence or want of a cartilage. 

 The greatest resemblance which I can find, as regards the structure and general 

 character of the shell of Glauconomya, is that with Standella (of the lvtrariin^) ; 

 the cartilage processes are, of course, very different, but there actually is a perfect 

 analogy between both in their position with reference to the external ligament. 



In habitat the GLAUCONOMYiDA^ixio^ilj resemble the Solenid^ ; both burrow 

 in sand and mud, and most of the species live in brackish water ; they appear to be 

 confined to the waters of the Eastern, especially the Indian seas. I have observed 

 several species of Glauconomya burrowed in sand between tide-marks ; they seemed 

 to prefer particularly those localities where a small stream of fresh water enters 

 upon the beach. Thus comparing all these characters of the shells and the 

 animals, I do not think they are in favour of the classification of the Glauconomyidm 

 in the VBNERA CJEA, but that they clearly indicate a position near the Saxicavid^, 

 forming in many respects a transition from these to the SolenijdjE, 



There are at present only two genera, Glauconomya and Tanysipho^i, sufficiently 

 well known to be placed in this family, but it appears to me probable that this 



