354 CONTRIBUTIONS TO THE NATURAL HISTORY 



difference between the longitudinal and transverse diameter is already more marked. 

 But what is more striking, a considerable portion of the body seems, still further, more 

 elongated than its general outline, and the four lateral lobes, or auricles, appear as ap- 

 pendages to the anterior and posterior lobes. In proportion, however, as the larger 

 lobes expand, the small lateral lobes are successively more and more detached from 

 them, and their real connection with the sides of the main body begins to be appar- 

 ent, as in Fig. 7, 8, and 9. In this position the greater length of the anterior and 

 posterior ambulacra, and the shortness of the lateral ones, are quite apparent. In pro- 

 portion as the anterior and posterior lobes are more and more stretched forwards and 

 backwards, their sides assume a more pointed form, similar to the horns of a crescent, 

 or rather to the blade of a tomahawk, and the whole body, from its diminutive size, 

 appears like two tomahawks in miniature placed head to head in opposite symmetrical 

 directions, without handles, the four short lateral appendages looking like two small 

 sticks projecting through the eye of the head for an equal length on both sides. 



Seen from below, in the same development of all parts, the general outlines do not 

 differ materially from the view just described, excepting that the mouth is in sight in 

 the centre, extending forwards and backwards in the same plane as the circumscribed 

 area opposite, and the ambulacra appear only indistinctly through the mass. Fig. 6 of 

 Plate VII. represents such a view. The body, however, is sometimes stretched in the 

 longitudinal diameter to such a degree as to give its outline an irregular, oblong-square 

 form (Plate VI. Fig. 10). 



Viewed in profile, the body presents also two very distinct aspects when seen by 

 the broad face or by the narrow face, or when examined from its anterior and posterior 

 or from its lateral side. Facing the anterior or posterior end, the symmetry of the 

 figure, as in Plate VII. Fig. 4, arises from the parity and symmetry of the right and 

 left halves of the body ; the two sides of the anterior and posterior lobes being per- 

 fectly symmetrical. But here, again, the outlines may differ greatly, in consequence 

 of the expansion or contraction of the lobes, which may hang down and look almost 

 straight, with the main mass of the body above, or spread laterally and assume a round- 

 ed form, like a broad apron suspended from the chest with projecting auricles or ap- 

 pendages about its point of insertion (Plate VI. Fig. 6). In this position the anterior 

 or posterior pairs of ambulacra are seen in their fullest development, extending from 

 the summit along the middle of the lobe to its lower margin, tapering gradually as 

 the lobes grow thinner. 



Seen from the sides, the symmetry of the figure arises from the perfect symmetry 

 and equality between the anterior and posterior extremity of the body, and the outlines 



