338 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.45. 



surface striae and in the number of its spines. Full-grown specimens 

 are frequently 20 mm. wide and generally not quite 10 mm. long. 

 The pedicle valve is gently convex; beak low; spines on the cardinal 

 margin from 12 to 16 and the radiating striae over 100 and occasionally 

 as many as 200 at the margin. A short median septum is generally 

 present under the beak of the pedicle valve. The brachial valve is 

 slightly concave. There is no enlarged median rib on the pedicle 

 valve, but occasionally a narrow median furrow crosses the shell at 

 this point. 



The shell differs from Chonetes nova scoticus Hall in its greater 

 transverse extension; ordinarily it is twice as wide as long. 



Locality. — Pembroke formation, Leighton Cove, Long Cove, and in 

 many other localities in the town of Pembroke. 



Cotypes—Qsit. Nos. 58960 and 58961, U.S.N.M. 



Genus CAMAROTCECHIA Hall and Clarke. 



CAMAROTCECHIA LEIGHTONI, new species. 

 Plate 30, figs. 9, 11, 12, 13. 



Cf. 1839. Terebratula lacunosa Soweeby, Sil. Syst., p. 611, pi. 5, fig. 19 (not 



T. lacunosa Schlotheim of p. 624, pi. 12, fig. 10). 

 Cf. 1848. Terebratula lewisi Davidson, Bull. Soc. Geol. France, ser. 2, vol. 5, 



p. 330, pi. 3, fig. 30. 



Subtrigonal, both valves convex and for the first f cm. of growth 

 nearly equally gibbous, the pedicle valve having a well-developed 

 overarching beak. The pedicle valve for the first half of growth 

 shows no distinguishable median sinus, but at the front and for a 

 quarter way back in full-grown shells a slight sinus is formed by the 

 depression of the central three plications and the prominence of the 

 plications bounding the sulcus; the lateral slope, however, is gradual, 

 the bounding plication not raised above the others. The plications 

 are 8 on each side the sinus and a trace of a ninth can be seen at the 

 extreme cardinal lateral angle of the shell. The plications and the 

 grooves between them are evenly rounded — not angular. In mature 

 shells of 1^ cm. length the plications for the first half are smooth on 

 molds of the interior, and exterior molds show only very fine concen- 

 tric lines. After mid-growth the plications are crossed by strong 

 lamellar concentric lines, about 0.5 mm. apart, and on occasional speci- 

 mens the change in mode of growth is marked by a strong line of 

 thickened shell depressing the forward part from the early shell growth, 

 as in specimens 10 and 1 on the slab with figured specunen (fig. 11). 

 The brachial valve has 4 plications raised above the general surface 

 from the middle to front, and 7 plications each side and in very 

 good specimens a trace of the eighth at the cardino-lateral angle. A 

 thin median septum cuts the beak of the brachial valve and reaches 

 to near the middle of the shell in molds of the interior. These charac- 



