482 MEMOIRS OF THE CARNEGIE MUSEUM. 



ing and flattening, and finally disappearing. These broad bars are conspicuous 

 chiefly immediately in front of the umbonal ridge, and are distinctly seen even in 

 our largest specimens, where the beaks are greatly eroded. All these bars are 

 smooth, except for the concentric striae of the epidermis which cut across them. 

 In some of my 3'oung specimens there are a few oblicjue wrinkles upon the posterior 

 slope, but there are hardly any radial bars, except one, fine, and short, close behind 

 the broad bars of the umbonal ridge. There is a narrow and short lunula in front 

 of the beaks. 



Epidermis smooth, but with numerous, irregular, concentric lines, which be- 

 come sublamellar upon the jjosterior slope and near the lower margin. There are 

 also numerous fine, irregular, but straight, radiating lines on the disk below the 

 beak-sculpture. The posterior slojie has no radial ridges or furrows. Color of 

 epidermis dark to light green, with concentric bands of yellow-brown. The three 

 young specimens are light golden-brown towards the beaks, and light green towards 

 the margins; in the old specimens the green color prevails, and becomes quite dark, 

 but is interrupted by one or two lighter bands of brownish. No traces of color- 

 rays present. 



Hinge-line almost straight or very gently curved. Ligamental sinus over the 

 posterior third of the lateral teeth. One lateral in the right, two in the left valve, 

 rather long, distinct, and in old shells gently curving downward behind. Pseudo- 

 cardinals very variable. Lea describes them as trifid in both valves, but this is 

 not always the case. Of our largest specimen it may be said that the right valve 

 has three teeth: the middle one the largest, directed obliquely downward and for- 

 ward, triangular, narrow above, broader below, and deeplj' longitudinall.y cleft 

 into three ridges; in front of it is an anterior, narrow, comjiressed tooth, which 

 is connected with the middle one above; behind the largest pseudocardinal is a 

 deep groove, followed b.y small, ragged elevation of the hinge-plate representing 

 the third tooth. The left valve has one large posterior tooth, which is ragged and 

 fits into the groove behind the middle tooth of the other valve (including the small 

 elevation behind it), and in front of it is a narrow lamellar tooth, fitting into the 

 space between the first and second teeth of the right valve. In the groove be- 

 tween these two teeth of the left valve are two low ridges, corresponding to the 

 clefts of the large tooth of the right valve. In our second largest specimen (No. 1) 

 the same general arrangement is seen, but the anterior tooth of the right valve is 

 very low, while the third (posterior) is more distinct and triangularly elevated. 

 The left valve has two teeth. All these teeth are much less ragged, and the clefts 

 of the middle tooth of the I'ight valve are lacking, and also the corresponding ac- 



