SCORPION F.S. i 



is very variable in form ; the flattisk area of it that lies immedi- 

 ately behind the joint of the movable finger, and usually rests upon 

 the ground, is called the underhand. This underhand is generally 

 separated externally from the upper side of the hand by a strong 

 crest or keel, the keel of the underhand. The upper side is some- 

 times evenly convex ; sometimes, however, its outer portion above 

 the keel of the underhand is flat and vertical, and its inner portion 

 flat and horizontal, the two areas cutting each other at right angles 

 and separated by a ridge or keel, called the finger-keel, because it 

 runs forwards on to the immovable finger. Frequently additional 

 keels are developed both upon the outer and upon the inner 

 portion of the upper surface. The upper surface is generally 

 bordered internally by a sharp edge, known as the inner edge- 

 or border, and the area beneath this edge and between it and the 

 underhand is called the inner or inferior surface of the hand. 



B. 



A. 



Fig. 2. — A, upper, and B, under 

 side of hand of Scorpiops orasamamis. 



a, outer portion of upper surface ; ft, 

 finger-keel ; c, inner portion of 

 upper surface : d, keel of under- 

 hand ; e, underhand : /, inner sur- 

 face of hand. 



.' / .->C 



a:. 



Fig. 3.— Movable finger of chela of 

 Lychas scutilus. 



a, external ; ft, median; e, internal 



series of teeth. 



according to its position when the hand is normally at rest, anil 

 according to the shape of the particular hand under description. 

 The movable and immovable fingers are provided with teeth along 

 their biting-edges. The arrangement of these teeth furnishes 

 valuable specific and generic characters. The armature tisualh 

 consists of several rows of small teeth arranged longitudinally and 

 partly obliquely along the middle line of the finger, sometimes set 

 end to end, sometimes overlapping to a greater or less extent. 

 These constitute the median series of teeth. Moreover, the anterior 

 tooth of each row of the median series is often enlarged ami 

 separated from the rest of the row to which it belongs. This 

 series of anterior teeth thus enlarged and often isolated constitutes 



