29 American East Coast Arcas 29 



America from Cape Cod to Yucatan. — Dall. Pliocene of the Croatan beds, North Caro- 

 lina: Pleistocene of Georgetown, South Carolina; of Crowley Oil Company and Knapp's 

 wells, Grand Chenier, and New Orleans, Louisiana: recent from Point au Fer, Louisiana; 

 Galveston, Texas; and Long Key, Cedar Keys and Ft. Barrance, Florida. — C. U. Museum. 



The Noiitias .show a variation which reaches an extreme in A. reversa Gray (Plate 

 VL Figiires 11, 12), from the west coast of tropical America. In A. incile the shell is 

 long with a long hinge-line and very anterior beaks. In typical limula the beaks are 

 nearly as anterior when distances are measured parallel to the base instead of parallel 

 to the hinge, but the hinge-line is much shorter so that the beaks are a comparatively 

 short distance in front of the center of the hinge. In A. pondcrosa both shell and hinge 

 are short and the beaks are opposite the center of the hinge. A. reversa is still shorter 

 and all the ligament area and nearly all the hinge are anterior to the beaks. With the 

 shortening of the hinge it has become wider, the line of teeth more curved and the 

 V-shaped teeth, which are inconspicuous in A. incile, have become more prominent; 

 the width of the bare strip behind the ligament has decreased; the shell has developed a 

 truncation so pronounced in A. reversa that the posterior parts of the two valves lie 

 nearly in the same plane. A. reversa, however, is probably not descended from the 

 other species mentioned. A. {No'ctia) modes/a Grzybowski, from the Tertiary of Peru, is 

 as short as reversa and the posterior part is concave. Grzybowski's A. reversa, from the 

 Tertiary of Peru, is much larger than the recent form. C. B. Adams, Carpenter, Kobelt 

 and Dall place A. hemicardiinn Koch in synonymy with A. reversa. 



A. tri?iitaria Guppj^; Plate VII, Figures i, 2; (Quart. Jour. Geol. Soc, vol. 22, p. 

 583, pi. 26, figs. 3a, 3b, 1866; Schuchert, U. S. Nat. Mus., Bull. no. 53, pt. i, p. 57, 

 1905), from Manzanilla, Trinidad, is very similar to A. reversa, but is smaller. It has 

 forty ribs and a fiat, cordate posterior portion. Dall (Wagner Free Inst. Sci., Trans., 

 vol. 3, p. 658) lists this species as Oligocene. A. centrota Guppy; Plate VII, Figure 3; 

 (Proc. Sci. Assoc. Trinidad, p. 175, Dec. 1867; Schuchert, U. S. Nat. Mus., Bull. no. 53, 

 pt. I, p. 55, 1905), fossil from Trinidad, also belongs to Noetia. It is given by Dall as 

 probably a Miocene species. The original description is repeated in Ann. Nat. Hist., 

 4th. ser., vol. 15, p. 51, 1875, and a figure is given in Geol. Mag., 1874, pi. 18, fig. 23. 

 It has 36-38 ribs with fine interstitial ribs in the narrow interspaces and there is an angle 

 in the posterior margin near the hinge. It is about 25 mm. long and resembles the 

 young of A. limula, but is nearer to A. Martinii Recluz. Specimens in the C. U. Mu- 

 seum from Maranhao, Brazil; Plate VII, Figures 4, 5; are evidently the recent species 

 which Guppy (Ann. Nat. Hist., 1875, p. 51, pi. 7, figs. 4a, 4b) collected from the Gulf of 

 Paria and referred to A. centrota. They also agree well with A. bisulcata Lamarck (An. 

 s. Vert., vol. 6, p. 45, 1819), and with A. Martinii Recluz (Jour, de Conch., vol. 3, p. 

 409, pi. 12, figs. 3, 4, 5, 1S52), from southern Brazil. Dall states that the name Martinii 

 is preoccupied by Bolten. The living species should probably receive the name bisulcata 

 with centrota as an ancestral form or possibly the same species. The Maranhao shells 

 have a small cardinal area not entirely covered by the ligament, the interspaces are 

 rather narrow and are. nearly filled by the fine interstitial ribs, the shell is often yellow 



