EDWARD S. MORSE ON 



secondly, that when iu the mature form, the setae are very short; in the young of all 

 species observed they are very long, often exceeding in length the shell (61) , notably 

 in Terebratulina (61: 16) and Hemithyris (61: 17). 



BKACHIA. 



The brachia form one of the most complex structures of the animal and, in life, one 

 of the most beautiful. In one division they are more or less rigidly held by the calcare- 

 ous loops or crura ; in the other division they have the greatest freedom of movement 

 within the pallia! cavity. No drawing can convey the grace and beauty of their various 

 motions; in one attitude suggesting the lophophore of the phylactolaematous Polyzoa, at 

 another time thrown into a position resembling that assumed by some sabelliform worm. 

 The attitudes of the brachia are constrained to a symmetrical position on either side of a 

 median line in those forms having crura; even the cirri seem to be controlled by this 

 bi-symmetrical impulse, though individual cirri often move more independently. Hemi- 

 thyri* jtxittacea was observed to move one coiled brachium beyond the shell in advance of 

 the other (46: 14). In the Lingulidae, the brachia have the greatest freedom of motion, 

 yet, so far as observed in life, the various attitudes are strictly bi-symmetrical. The veil or 

 collar at the base of the cirri is brown, being lighter or darker in different species ; the 

 brachia are pure white, and the cirri are variously colored with brown pigmentation. The 

 various attitudes of the bracliia in G. pyramidata are depicted on 45. Under a low power 

 they present attitudes of the most exquisite grace and beauty ; the brachia coil and uncoil 

 with the greatest freedom, and sometimes the cirri stretch quite to the anterior borders of 

 the shell and even a little beyond (45: 13) ; again the coils are depressed like a flat helix 

 and gradually change their position, assuming the attitude of a globular helix with high 

 spire. The axis of this helix is often changed, sometimes standing nearly vertical and 

 then taking a nearly horizontal position, these attitudes being duplicated with perfect 

 symmetry by the two bracliia. A characteristic and beautiful attitude of the brachia of 

 ( ilottidia is figured on 45: 6. This attitude is assumed when the animal is at rest, with the 

 anterior part of the body slightly protruding from the sand. The entire width of the 

 pallia! chamber is occupied by the out-stretched cirri. In this figure the gill ampullae 

 may be seen projecting from the pallium above and below. The double flexure of the 

 anterior margins of the pallium is richly colored a dark brown, and later I shall suggest 

 that these are sensory regions susceptible to light impressions. The drawing but faintly 

 represents the surpassing grace and beauty of the extended arms ; the faint brownish 

 tinge of the cirri, the rich brown border of the brachia contrasting with the pure white 



