56 CEETACEOUS PELECYPODA 



8. — To this, M. Bebeyana {Card. Deheyanum, MiillerJ has to be added (see Bosquet in 

 Staring^s Bodem van Nederland, ii deel). I have examined a specimen obtained from Dr. Bosquet 

 himself, and it shows the species to belong* to ScJiizodesma, a sub-genus of Mactra, 



9. — To the same sub-genus also belongs the Aachen species which Miiller and Bosquet identify 

 with S o werby^s Mactra angulata. It is, however, undoubtedly distinct from it, much longer and propor- 

 tionately flatter, the posterior side shorter and rounded, the anterior longer and angular. It much 

 resembles our Indian if. tripartita, which, as regards form, also differs from Sowerby-'s J^f. angulata 

 as well as by a posterior ridge and stronger concentric ribbing. I propose to call the Aachen 

 species M. Bosquetiana -, it belongs to the sub-genus Schizodesma, 



10-11. — M, JDidonis an^ MiEvusi of Coquand are from Algiers; they are rather globose, like 

 Poromyce ; the hinges are not known. 



ia-17.— From North America Meek in his Check List (Smith. Misc. Coll., No. 177, 1864,) 

 quoted the following species, M. lataj/ormosa, gracilis, siouxensis, texana and Warrenana. 



18. — Gabb (PaL Calif., 1864, 1, p. 153,) describes if. fCymhophoraJ Ashhurfierii. Mr. Gabb says 

 this "^ is one of the most common fossils in the state."'' Mactra alharia (Cheek List, &c., Smithson. 

 Misc. Coll., No. 200, 1866, p. 8,) from the so-called lower eocene rocks will probably be added 

 to the list. 



19.— if. Araucana, d'Orb. (Voy. Astrolabe, Pal., pi. II, figs. 2-4,) is, as to external form, a 

 typical species of a Mactrella. 



? 20-21. — M. Araucana 2iTA Cecileana ^YQ^x^\, described by d^Orbigny (Voy. Ameriq. merid. 

 pp. 125 and 126, pi. XV, figs. 3-6,) as coming from tertiary deposits of the island Quiriquina. 

 With these two he also describes (ibid. p. 125) a M. Aiica from Coquimbo north of Chili. This last 

 species I would rather consider as a Feriploma or a Corimya. The first named two. are subsequently 

 placed by the same author (Prod. II, p. 235,) in the Senonien, which, judging from the other species 

 occurring with them, appears to be quite correct. M. d^Orbigny does not, however, state whether 

 he considers the Astrolabe M, Araucana to be the same as that described in the Voy. Am. merid. 

 The figures, if correct, would indicate two distinct species, the second having the shorter (posterior ?) 

 side roundish, and the longer (anterior) subcarinated, while the opposite is the case in the 

 former. 



22. — M, CJiilensis, Gabb, is also from Chili. 



23-26. — M. petrosa, pervetus, arciformis, and syriaca are described by Conrad in the official 

 report of Lynch's expedition to Palestine. They are only based upon casts, and therefore doubtful 

 as to generic and, if Fraas be correct, even as to specific determination. 



27. — if. tripartita is the only species from our South Indian cretaceous deposits, the 

 Jf. intersecta (Cardium idem, apud Forbes), beiug to all appearance only a variety of the same, as I 

 shall presently explain. 



MACTRA, Linn., 1765. 



If we were allowed to draw a conclusion from the three cretaceous species 

 which unquestionably belong to Mactra, there is reason to state that the sub-genus 

 Schizodesma is the most prevalent, a form which is also numerously represented in 

 the present seas. 



