232 



Annals of the Carnegie Museum. 



across the area to the apex, and is probably the path of the anal tube. 

 On either side of the cardinal process is a narrow dental socket, bounded 

 by two low plates. The four adductor scars lie directly in front of 

 the cardinal process. By the sides of the anterior pair are high di- 

 vergent ridges somewhat like those in Stropheodonta inaqiiistriata 

 of the Hamilton. Dividing the anterior pair of adductor scars is a 

 very low and thin median septum. Outside the area involved in the 

 muscular attachment the interior of the valve is thickly covered with 

 sharp spinules, which are directed forward. These spinules are arranged 

 in radiating rows, and do not extend beyond the line at which the \alve 

 is deflected. Along the crest of the fold in the shell are radial grooves, 

 seemingly indicating that the mantle of the animal was thrown into 



3 4 . 5 



Fig. 3. Outline of the specimen shown in fig. 32, Plate XXXIV, to show cur- 

 vature of the shell. 



Fig. 4. Leptmna incrassata 'H.a.W. Both valves of a very young specimen. X2. 

 Fig. 5. The same species. Drawing of the specimen shown in fig. 34, Plate 

 XXXIV. X 2. 



a series of radial folds in order to accomplish the deflection. Such 

 abrupt turns in brachiopod shells have been explained by saying that 

 one valve grew faster than the other, but this in turn requires an ex- 

 planation of the cause of the acceleration of growth. In the present 

 case there might be an explanation in the fact that as the shell in- 

 creased in size and weight, there would come a time when the small 

 pedicle could no longer support the shell in an upright position, and 

 the shell would fall back upon the heavier (pedicle) valve. Then, in 

 order to keep the opening of the valve free, there would be a constant 

 upward turning of the edge of the mantle, and consequently a change 

 in the direction of the new shell deposited after the change of position. 

 Locality. — This shell is very common at Sloop Island, Valcour 

 Island, and Chazy, New York. A few specimens have been found at 

 Crown Point and Cooperville, New York. 



