56 CEETACEOUS PELECYPODA 



8. To this, if/. Beheyana {Card. Bcbeijanum, Muller,) has to l)e added (see Bosquet in 



Staring's Bodem van Nedeiland, ii duel). I have examined a specimen obtained from Dr. Bosquet 

 himself, and it shows the species to belong to Schizodesma, a sub-genus of Mactra. 



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



with Sowerb/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 mucli 

 resembles our Indian J/, tripartita, which, as regards form, also differs from Sovverby's J/, angulata 

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

 species M. Bosqiietiana ; it belongs to the sub-genus Schizodesma. 



10-11. — M. Bidonis ixnA ihevusi of Coquand are from Algiers; they are rather globose, like 

 PoromycB ; the hinges are not known. 



12.17. — From North America Meek in his Check List (Smith. Misc. Coll., No. 177, 1804,) 

 quoted the following species, M. lata,formosa, gracilis, siouxensis, texana and Warreiiana. 



18. Gabb (Pal. Calif., 1864, 1, p. 153,) describes M. (Cymhoplwra) A-Murnerii. Mr. Gabb says 



this "is one of the most common fossils in the state.'' Mactra albaria (Check List, &c., Smitlisou. 

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



to the list. 



19.— 3f. 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 sio.^ Cecileana&re ^rst 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 be also describes (ibid. p. 125) a M. Auca from Coquimbo north of Chili. This last 

 species I would rather consider as a Periploma or a Corimija. 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. Chilensis, 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. — M. tripartita is the only species from our South Indian cretaceous deposits, the 

 M. intersecta (Cardium idem, apud Forbes), being 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 tlii-ee 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. 



