14 bulletin: museum of comparative zoology. 



Triplegia cuspidata (Hall). 



Plate 1, fig. 1-6. 



Atrypa cuspidata Hall, Pal. N. Y., 1847, 1, p. 138, 318, pi. 33* (supplementary 



plate), fig. la-h: Hall & Clarke, Pal. N. Y., 1892, 8, pt. 1, p. 270. 

 Triplecia extans Hall & Clarke, Loc. cit, 1892, pi. lie, fig. 1-3. 



Without exception, Triplecia cuspidata is the most abundant fossil 

 in the basal ten feet of the Trenton at Martinsburg, and a large num- 

 ber of complete specimens retaining both valves were collected. Most 

 are large, specimens 18 mm. long and 25 mm. wide being common. 

 Smaller specimens are also present in some numbers, but not the very 

 young. Two specimens, one 9 mm. by 11 mm., another 20 mm. by 28 

 mm., probably represent the extremes of the range in size. The 

 smaller of these is 6 mm. thick, the larger 17 mm. It proves in 

 practice somewhat difficult to separate the various species of Triplecia. 

 It will be remembered that Hall, at the end of his first work on 

 Trenton fossils, came to the conclusion that Atnjpa extans and Atrypa 

 cuspidata were identical. Triplecia nucha is easily recognized by its 

 small size, sharp, narrow fold and sinus, and absence of radial striae. 

 Triplecia extans and T. cuspidata are both striate, the latter much more 

 strikingly so than the former. After examining a large number of 

 specimens from Watertown, Martinsburg, Trenton Falls, and else- 

 where, it would appear that T. extans is characterized by a rounded 

 sinus, T. cuspidata by an angular or grooved sinus, and a new species, 

 now to be named, by a flat-bottomed sinus. 



In my judgment, one of the specimens figured by Hall and Clark 

 as Trijilecia extans, is a very typical T. cuspidata, and I have so as- 

 signed it above. It displays the typical angular sinus. Figures 6 

 and 7 of the same plate show the rounded sinus of T. extans. 



The exact horizon at which the various species of Triplecia occur 

 has not yet been determined. Hall stated that T. cuspidata was 

 known to him as occurring only in the central part of the Trenton 

 limestone at Lowville, a town only five miles north of Martinsburg. 

 I^did not have time to search for the original locality, but from the 

 nearness of Lowville to Martinsburg it seems probable that the 

 original specimens were really from the base of the Trenton, which is 

 the only horizon in which this species is found at Martinsburg. In 

 the M. C. Z. there are a great many specimens of this species from 

 Watertown, N. Y., but unfortunately without exact data as to the 

 horizon in the Trenton from which they were obtained. There are 



