334 ■ EDWARD S. MORSE ON 



to move the several parts, but special muscles — the retractor hrachia — are found which 

 would seem to indicate a considerable movement of the structure as a whole. It is highly 

 probalde that the brachia have the power of uncoiling and even of partially projecting 

 from the pallial chamber. The vai'ious muscles at the base of the cirri and of the collar 

 indicate the same mobility of parts as is found in the Lingulidae. In 46: 10, is represented 

 a section of the bracluum of 2). lameUosa at a point indicated by A, B iu 49: '2. In the 

 sinus at the base of the brachium, which is named the small brachial sinus Ijy Blochmann, 

 curious little round cells occur, held together by delicate threads ; their function is not 

 known, though they may be what Blochmann terms, in this region, gland cells. At 

 46: lOn is a greatly enlarged view of the appearance of these bodies. 



In Teri'hratulhia septentr'ionaUs, three millimeters long, the cirri project slightly 

 beyond the borders of the shell (46: 12). Barrett ('55) has already observed the same in 

 the adult form. In TerehrataUa coreanica (46: 13), the cirri reach quite to the inner 

 borders of the shell but were not observed to go beyond this edge. In all those forms 

 with crura the brachia are constrained to a more or less rigid attitude, yet there must 

 be some elasticity in the anterior portion of the brachia. 



In Jlemithyris ps'dtacea, the brachium forms a coil of many turns. As I have shown 

 elsewhere ('78), the brachia are at times protruded in a coiled condition (46:14). In 

 this figure it will be seen that oue coil is projected farther than the otlier, indicating an 

 independent motion of the brachia. In Ilemithyris alhida, dredged in Tsugaru straits, 

 between Yeso and Japan, the brachia were observed protruding in the same way. One 

 inchvidual, with the coils protruded, was suddenly immersed in alcohol auil the left 

 brachium immediately uncoiled to nearly its full length, as shown in 46: l.J. Iu //. j>.s';7- 

 tacea the brachia may be partly uncoiled within the pallial chamber as shown in 46: 16, 

 and it would not l)e surprising if, under certain conditions, the lirachia might uncoil 

 and be protruded as shown iu the alcoholic specimens above mentioned. The free collar 

 about the mouth is very mobile (46: 17, 17«)? and just above the mouth a white, fibrous 

 yoke is seen connecting the base of the In-achia. A rounded area which appears on each 

 side of this yoke indicates the great sinus connecting the brachia with the coelomic cavity. 



The cirri, though apparently rigid, do move with great freedom. The general 

 appearance, as they spring in double and alternating series from the brachium, is shown 

 iu 46: 18. The margin from which they spring is scalloped, and tiie cii-ri rise from the 

 crests of these scallops. Scattered muscle fibres are detected running to the scalloped 

 margin, and parallel with this margin are other bands of muscle filn-es. 



