14 CEETACEOUS PELECYPODA 



8. Polarthiis, Gabb, {vide Check-list of the Invertebrate foss. of North 

 America; Smithson. Misc. Coll., No. 177, p. 16, 1861). This has been based upon a 

 cretaceous species, P. americanus, from New Jersey, but I have not been able to 

 get access to any detailed statement regarding the distinctive characters of the 

 genus. 



It does not appear quite certain whether the distinctions pointed out as exist- 

 ing in the shape of the palettes of the first three genera are sufficient to warrant 

 the above-mentioned divisions ; they may all be considered as slight variations of 

 one and the same genus. Teredo, l)ut of the three other groups the palettes seem to 

 be sufficiently distinct, though, no doubt, passages from one into the other, — as, for 

 instance, between NausUoria and Xylotrya—, may readily be observed. 



Tryoii (Am. Jouni. Con(-h., vol. iii, ^rt. 3, 1867,) enumerates 31 recent species of TEREdinin^. 

 From tertiary deposits about 15 species are known, and from the cretaceous* Pictct (Mat. p. 1. 

 Paleont. Suisse, 4'"'' Ser. ; Foss. St. Croix, ^^'^ part., No. 1, p. 21, &e.,) quotes seven European 

 species; T. Argonensis, Varennensis, lilobaius, Fleuriatisus, liequienianus, Deshai/esi anik rolnndalus ; 

 several of them are, however, very unsatisfactorily recorded. Coquand described a Ter. I'ujni- 

 tortim from the etage Aptien of Spain (Mon. de FAptien, etc., 1865, p. 87). Schafhseutl 

 in his Siid-Bayern's Leth. Geognostica, 1863, (pp. 177 and 178) names two tubes, Teredo 

 ( GasirochcenaJ ornata and rugosa, respectively; as he identifies other fossils, apparently occurring in 

 the same beds as these two, with known cretaceous species, one must suppose that the former are also 

 cretaceous; no distinct proof, however, is given of their geological position. 



Eichwald in his Leth. Rossica, livr. xi, 1867, (p. 792, etc.,) describes under the generic name 

 of Teredo six species which, he states, all occur in cretaceous deposits. Of none of them have the 

 valves been noticed, and the tubes of some appear rather defective. Teredo Tournali is identified 

 with a species described by Leymerie from supposed nummulitic beds. T. Argonensis, Buv., is deter- 

 mined from a small tube which does not very well agree with Buvignier's and d'Orbiguy's figures. 

 The others are new, T. sulcala, lignicola, cohuIhs, and socialis. Of the first the representation may be 

 taken rather for that of a GastrocJicena than of a Teredo. The tubes of the two last named, 

 and especially that of T. conulus, greatly resemble in general form the short tubes described by 

 Deshayes as TeredoUles davatiis. It is quite possible,- if not more probable-, that these tubes were 

 made by shells of the pboladlvje, or by a Gastrochana, for they occur socially, often in great numbers, 

 and bored for only a short distance into the wood, as the Marlesue, &c., generally do at the present 

 time ; but they are somewhat thickened and blunt at the anterior end, a form more usually occurring 

 in the TEREDININ.E than in the pholadin^E, though not quite foreign to the latter. Zittel in his 

 Monograph of the Pelecypoda (Bivalves) of the Alpine Gosau-formation (Denksch. Acad., Wien, 

 1865, vol. xxiv,) does not describe any species of Puoladid.e. As far as I remember, vegetable 

 remains, bored by them, were repeatedly found in the coal beds of the so-called " Neue-Wclt " near 

 Wiener Neustadt, and we may expect some additions to the cretaceous fauna fi'om this quarter. 



The fragment of a tube figured by Rcimer (Noi-d-deutsches Kreidegeb., pi. 10, fig. 9,) as 

 T. dentatm is much like that of a tube of a Teredina, while the IVlastricht Teredo Faujasi of Bronn 

 seems more likely to be a serpuloid shell than a Teredo ; numerous fragments of wood, however, occur in 

 the Mastricht beds, entirely bored by true teredimnje. The tubes so commonly known from the 

 German cretaceous deposits as Gastrochcena (ox Serpula) amjjhisbmna, Goldf., are most likely those 

 of a species of Teredo or Teredina ; they are much too long for a Gastrochana, and also too regularly 



* Teredo Argonensis, Buviguicr, is probably a Turnus, whicb genus may also belong to this sub-farail3-. 



