LIVING BRACHIOPODA. 331 



adhesion of this matter. In D. lamellosct a rich growth of organisms abounds, and even 

 in young Terebratulina the inactivity of the setae permits this accumulation of foreign 

 substances. In the mature D. fumi'l/oxa the setae are rich light brown in color; they 

 are closely crowded together about the entire periphery of the pallium, though not so 

 thickly massed on the posterior border and being in this region only ^ the length of the 

 shell, while on the anterior border they attain the length of the shell (49: 12). They are 

 mostly barbed, rarely smooth (44: 7). In the young of D. faineUosa, the setae are much 

 longer than the diameter of the shell, becoming shorter on the posterior border or quite 

 absent (61: 5, 9, 11, 12). Some are furnished with short bristles on the sides of the setae, 

 and these setae are thicker and are not so deeply buried in the pallium as the more deli- 

 cate setae which are furnished with long hair-like setellae (44: 9) and in rare instances 

 more delicate setellae branching from these (44: r>). The setellae are bent at their junc- 

 tion with the setae, and those nearest the border of the pallium are bent backward. 

 Joubiu ('86) figures the setellae before they have issued from the pallium, as pointing 

 in the same direction as the growth of the setae. This attitude would be manifestly 

 impossible unless a sheath, enclosing the whole seta with its branches, moved outward in 

 its growth from the follicle. On the contrary, the setellae trail backward in the growth of 

 the seta and, after issuing from the border of the pallium, preserve for some time the bent 

 attitude they had while immersed in the pallium (44: 8). Blochmann has figured their 

 appearance correctly. 



.In T. septentrionalis, the longitudinal ribbing of the shell corresponds to the number 

 of setae ; that is to say, at the marginal termination of every rib of the shell a seta pro- 

 jects; this is especially marked in the early stages of the animal. In Terebratalia core- 

 anlca, the border of the pallial membrane is light rose-color and the setae and follicles are 

 light yellow (39: 11). The setae are very short, hardly extending beyond the margin of 

 the shell, and are embedded at various depths in the pallium. They are somewhat apart 

 from one another (44: 1:2) . In Terebratalia minor, the setae are extremely short and are 

 quite widely separated from one another (44: 13). InLaqueus ntbellus the setae are very 

 short and the transverse marks upon them are much farther apart than in the other 

 forms studied (44: 14). In Hemitkyris psittacea, the setae are very short, delicate, and 

 very brittle ; the setigerous follicles are only slightly enlarged at their base. Two and 

 even three setae apparently spring from one follicle. Between the follicles are threads 

 of binding tissue and what appear to be muscular fibres (44: 15). 



In summing up this brief examination of the various forms of setae here studied, it 

 may be stated, first, that in every instance the setae are longest on the anterior border of 

 the pallium, diminishing gradually in length around the lateral border and being shortest 

 around the posterior border where they are tenuous, brittle, and often bent and broken; 



