correspondingly from each side, with the T-shaped posterior end of the 

 T-shaped posterior end of the basic middle plate. At the place of the 

 sharp curvature of the lateral anterior plates they form a more or less 

 clearly expressed little hump which serves for articulation with the "lateral 

 middle" plates (Fig. 303, E and F). The latter, starting from the above- 

 mentioned hump of the lateral anterior plates, extend along the edges of the 

 clamp posteriorly and terminate approximately at the three-quarter level 

 of the total circumference of the clamp. Somewhat lower and also along 

 the edge begin the paired "posterior lateral" plates (Fig. 303, G and H) 

 which terminate, articulating with the posterior end of the supplementary 

 middle plate. As is seen from the description, the lateral anterior plates 

 are equivalent to the lateral plates of the anterior valve of the clainps of 

 Discocotylidae and are undoubtedly homologous to thenn. As regards the 

 middle and posterior lateral plates, they correspond together to the lateral 

 plates of the posterior valve of the clamp of Discocotylidae but it is not 

 clear whether they are all homologous to these plates and, in other words, 

 whether there is one lateral plate divided into two parts on each side, or 

 whether here occurs a new formation of an extra pair of lateral plates. 



Along with the above-mentioned 8 skeletal parts the posterior 

 half of the clamp bear? a number of cuticular thin sticks lying in parallel 

 rows on the interior surface of the right and left quarters formed by the 

 basic plates. The musculature of the clamps is rather powerful. The 

 cluster of the inuscles extending from the peduncle on which a clamp is 

 located lies almost in the middle and terminates in the clamp, attaching 

 itself to a special crest on the dorsal side of the anterior end of the basic 

 middle plate. In the more open position the clamp nevertheless appears 

 in the shape of an ordinary cup- -its anterior part is always more or less 

 curved toward the ventral side, as a result of which the basic middle plate 

 resembles a constantly bent spring just as among the preceding families. 



We observe further morphological changes in the structure of 

 the clamps of the Diclidophoridae among the representatives of Choricotyle 

 in which a different degree of asymmetry of separate elements with the 

 i^etention of the same number of basic chitinous plates (Fig. 304) is 



observed. Thus, the basic middle plate has the upper and the lower T- 

 shaped outgrowths with differently developed right and left halves. At the 

 same time the lateral anterior plates also become different. One of them 

 becomes considerably larger and of somewhat different shape than the 

 other (Fig. 304, C and D) as a result of which the clamp acquires a rather 

 marked asymmetry of the right and left halves. With this, in respect to the p. 434 

 longitudinal axis of the body of the animal, that side of the clamp which 

 lies outwardly (that is to the right from the right side of the body, and the 

 left from the left) has a large anterior lateral plate and perhaps both re- 

 maining ones. The muscular cluster extending into the clamps from the 

 "peduncle" in connection with this is nevertheless also displaced and 

 approaches from the ventral side which is more weakly developed. As a 



519 



