ACROTRETID^. 691 



Lingulellaf inflata ovalis Matthew, 1895, Trans. New York Acad. Sci. for 1894-95, vol. 14, p. 127, PI. V, figs. 4a-c. 

 (Described and discussed as a new variety. The specimen represented by figs. 4a-c is redrawn in this mono- 

 graph, PI. LXXVI, fig. 2a.) 

 Lingulella? inflataM.A.n'KEw , 1898, Trans. Roy. Soc. Canada for 1898, 2dser., vol. 4, sec. 4, No. 2, p. 128. (Mentioned.) 

 Acrothyra? inflata Matthew, 1901, Bull. Nat. Hist. Soc. New Brunswick, vol. 4, pt. 4, No. 19, p. 304. (Merely suggests 



change in generic reference.) 

 Lingulella {Acrothyra?) inflata Matthew, 1902, idem, vol. 4, pt. 5, No. 20, p. 390. (Mentioned.) 

 Acrotreta inflata (Matthew), Walcott, 1902, Proc. U. S. Nat. Mus., vol. 25, pp. 588-589. (Described essentially as 

 below.) 



Shell subcircular to transversely broad oval. Ventral valve subconical, with the apex 

 directed backward and usually on a line with the posterior margin, or extending beyond it 

 (PL LXXVI, figs. 1' and la'), but it may be anterior to it (PI. LXXVI, figs, lb' and Id'); 

 false area slightlj^ defined by the abrupt curvature of the cardinal slopes, median line depressed, 

 narrow, the two sides of the false area incurving to form it (PI. LXXVI, fig. Ig); pedicle 

 aperture longitudinally oval and slightly truncating the apex. Dorsal valve gently convex, 

 with a minute marginal beak. Surface of shell marked by concentric stride and growth lines, 

 and fine, irregular, wavy striae that inosculate more or less, giving the surface a fretted appear- 

 ance under a strong lens. The inner surface is marked by concentric lines and rather strong 

 radiating lines. The shell is built up of a thin outer ornamented surface and several thin 

 inner layers or lamellae. The average length of the ventral valve is 4 mm. and the width 3 to 

 3.5 mm. The dorsal valves are usually wider than long. Casts of the interior of the ventral 

 valve show strong cardinal scars, a strong apical callosity, and rather weakly developed main 

 vascular sinuses. The apical callosity varies in size and in form from elongate oval (PI. LXXVI, 

 fig. lb) to subcircular (fig. If). The cast of the interior of the dorsal valve shows large cardinal 

 muscle scars, and a broad, short median ridge posteriorly that extends beyond the center of 

 the valve. 



Observations. — This species appears to be a true Acrotreta with the apical callosity elon- 

 gated by the elongation of the ventral valve. The dorsal valve is more convex than in most 

 species of Acrotreta, which gives a stronger relief to the ridges on the cast between the cardinal 

 scars and the median ridge. The posterior view (PL LXXVI, fig. Ik') should be compared 

 with the same view of the dorsal valve of Acrotreta sagittalis (Salter) and its varieties (PL 

 LXXI, figs. 11', Im', and 3g"; and PL LXXII, figs, le' and If). The fretted surface is of 

 the same type as that of several other species of the genus. 



Matthew had very little material when he described the species [1886, p. 33]; subsequently 

 [1895a, p. 127] he created the variety ovalis from a more elongated ventral valve. In the col- 

 lection made for the United States National Museum by Loper, there are a number of ventral 

 and dorsal valves. The range of variation in outline appears to cover the variety ovalis. 

 Some are more transverse than the original type of the species and others nearly as elongate 

 as the variety ovalis. I have therefore considered the variety as within the original species. 

 Some of the shells show elongation and others are broadened by distortion. 



Matthew [1895a, p. 127] called attention to the resemblance of this species to Linnarssonia 

 and Acrotreta, and when describing the genus Acrothyra suggested [1901b, p. 304] that it might 

 belong to that genus. It appears, however, to be a true Acrotreta. A series of specimens, sup- 

 plemented by the types and a number of ventral valves received from Doctor Matthew which 

 he had [1895a, p. 126] provisionally identified as ^'Acrotreta gemma Bilhngs?" show a rather 

 repaarkable variation in outline and position of the apex of the ventral valve. This is illus- 

 trated by the figures on Plate LXXVI, also by a number of specimens not illustrated. The 

 narrow forms, var. ovalis Matthew, have the apex extended beyond the posterior margin, 

 and in the broad forms the apex is above or in advance of the posterior margin, but if the 

 shells are compressed vertically the apex may be pushed out over the false area whether the 

 shell be narrow or broad. I think that in the normal form the false area is vertical or slightly 

 inclined backward. 



Formation and locality. — Middle Cambrian: (2f and 2g)a Sandstones of Division Ibl of Matthew's [1895a, 

 p. 108] Protolenii^ zone, Hanford Brook, St. John County, New Brunswick, Canada. 



a The specimens in the United States National Museum collections to which these numbers are assigned were collected at the type locality 

 but later than the type specimens. 



