into two parts — an upper and a lower; the upper portion is 

 ordinarily developed as a broad lobe (1), armed on its upper 

 edge with a row of very long, stiiF bristles, pointing backward, 

 not exhibited in the drawings; it has a tendency to expand in two 

 directions, farming v.hat we have called the upper and hind processes 

 (up, up', hp, hp'), according to their position; the lobe is generally 

 smaller in tlie left clasp than the right; and the hind process 

 either wanting or minute upon the left. The lower part of the clasp 

 is a very long, slender, usually compressed, often twisted and invari- 

 ably curving blade (b, b'), frequently spined or pointed at tip, its 

 origin marked below by a denticle; it bears, at the base of the upper 

 edge, a short, frequently bent or curving process (p), ordinarily 

 somewhat triangular in shape, and very often armed with spinules; 

 sometimes (as in N. (rinds) this process is wanting on the right clasp, 

 and is usually more slender and frequently lonii^er on the left than on 

 the opposite side; at their base the clasps form a large, broad, com- 

 pressed, somewhat gibbous plate. 



The upper organ, Fig. Id. U, is much more difficult to describe. It 

 caries exceedingly in shape, so that one has to examine the parts 

 carefully, and through a considerable series to determine with cer- 

 tainty the homologous areas. It also differs much in size, in which 

 particular it appears to bear an inverse ratio to the dimensions of the 

 clasps. In general, it may be said to consist of a gibbous, subovoid 

 main body, contracted toward the tip, and bearing at the extremity a 

 pair of hooks, (h, h'), cccasionallj consolidated at the inferior junction 

 of which a minute, appressed, central plate, or tooth (t), dentiform 

 on a side vi<jw, frequently depends; near the middle of the upper 

 portion of the main body, the surface is either simply a little ele- 

 vated, or expanded after elevation into nearly horizontal alations; 

 or it rises into a dorsal, usually horse-shoe shaped crest (c), the 

 sides of which sometimes form conspicuous lateral expansions (c, e'), 

 the whole crest being frequently asymmetrical in elevation and lat- 

 eral extension, and bearing on its upper edge, or surface, an armature 

 of spines; from the middle of the upper surftice, lateral arms (a, a') 

 extend downward and then curve backward, meeting behind, and 

 at their united extremities expanding into a transverse, usually bi'oad 

 field, which we have termed the inferior armature (ia), well pro- 

 vided with spines or bristles. 



The movement of the clasps is of course lateral, and that of the 

 upper organ vertical; but some of the constituent parts of the latter 



