OF SOUTHEEN INDIA. 19 



has also been supposed to belong to TerecUna, is more likely a Fholudidea or a 

 Martesia ; it will be noticed subsequently under the name of Ph. Bomeri. 



2. Xylopharja, Turton, 1822. Valves Teredo- lilce, semi-oval, strongly gaping 

 in front, less so behind ; each valve with an internal rib running from the apex to 

 the periphery ; two j^re-umbonal accessory valves present. 



Three recent and a few tertiary sj^ecies of this genus are upon record. Two 

 species were formerly described under this genus from the cretaceous rocks of North 

 America, but for each of these distinct generic denominations have lately been 

 introduced. 



3. Goniochasma, Meek, 1864, (Smith. Misc. Coll., No. 177, p. 34). The 

 type is Xyloph. Siimjysoni, Meek and Hayden ; it is said to differ from Martesia by 

 the want of accessory "2)ieces" (valves?), and in having the anterior hiatus 

 formed by a rectangular notch in the antero-ventral margin of each valve. 



4. Tumus, Gabb, 1864, (Palseont. of California, vol. i, p. 145). The shell 

 is like that of XylophaQct, but has posterior to the internal umbonal rib another, 

 often broader rib, running from behind the apes towards the infero-posterior margin. 

 The animal also secretes a shelly tube, and consequently the valves must have been 

 much more gaping posteriorly than they are in the recent Xylophagce, which only 

 slightly protrude out of their shells. The accessory valves are unknown, and it is 

 therefore difiicult to classify exactly the genus, for it may be just as possible,- 

 and I would almost consider it more probable,- that it is a form of the teredinin^. 

 Gabb describes one cretaceous species (loc. cit., p. 146, pi. 22, fig. 116), T. jjlenus, and 

 I shall have to notice a second species of the same genus from our Southern Indian 

 cretaceous rocks, T. lapidarius, n. sp. Teredo Argonensis, Buvignier, may be a 

 thu'd species of this genus, and as regards the form of the shell itself it closely resem- 

 bles the last named one. Eichwald in his Lethtea Ross., (livr. xi, 1867, p. 790, 

 pi. 22, fig. 13,) states that Pholas Waldheimii, d'Orb., occm's in the Neocomien 

 at Kborosch6wo near Moscow ; the species secretes a solid shelly tube, and has on 

 its valves two ribs running from the apex to the periphery, like Tarims, but the 

 anterior portion of the shell would appear to show a great resemblance to a Martesia ; 

 it may be a Parapholas. 



4«. The genus Xylopliagella was proposed by Meek in 1864 (Smith. Misc. 

 Coll., No. 177, p. 34,) for Xylophaga elegantula of Meek and Hayden, which is 

 said to differ from Xylophaga by the presence of a "postero-dorsal ridge;" I presume, 

 therefore, that it is very closely allied to or generically identical with Tumus, but 

 Meek adds, that it " burrows apparently always without a shelly lining." This 

 would be a slight distinction from Turmis, but it requires confirmation, though I 

 must say that it does not seem advisable to attach too much importance to the 

 presence or want of a shelly tube. Many other prolavin^ give a proof of this, 

 secreting a perfect tube whenever they find a special necessity for it ; in other cases 

 they line the hollow excavated by them, only with a very thin shelly layer, and again 

 in others they secrete it only partially, for instance, on each tm-n of the 

 tube. 



