. Bulletin - United States National Museum. Science. 112 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. strong basal sphincter lies in the upper lip. This divides ventrally into two branches, an anterior, smaller, which gives rise to a fourth sphincter of the lower lip, and a broad posterior branch which Streiff regards as one of two divisions of the intermediate muscle (his "Bogenmuskel") but it seems rather to be comparable to such a ventral extension of the posterior dorsal lip sphincter as we see in Cyclosalpa. (See figures of both solitary and aggregated forms of Cyclosalpa on pla
. Bulletin - United States National Museum. Science. 112 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. strong basal sphincter lies in the upper lip. This divides ventrally into two branches, an anterior, smaller, which gives rise to a fourth sphincter of the lower lip, and a broad posterior branch which Streiff regards as one of two divisions of the intermediate muscle (his "Bogenmuskel") but it seems rather to be comparable to such a ventral extension of the posterior dorsal lip sphincter as we see in Cyclosalpa. (See figures of both solitary and aggregated forms of Cyclosalpa on plates 1 to 13.) The dorsal horizontal bands are present in the usual position (fig. 104). The atrial musculature (fig. 106) is a good deal like that of Iasis zonaria. Both species have a peculiar triangular area of modified test, in a valve-like posi- tion on the dorsal side of the atrial siphon. There is a well developed atrial retractor muscle, which is connected at the angles of the atrial aperture with the broad third sphincter of the upper atrial lip and with a ventral branch which soon divides to form the first and third sphincters of the lower atrial lip. There is a strong continuous band of muscle which forms the broad (fourth) sphinc- ter of the dorsal lip and fo. - the second sphincter of the ventral lip. The first FlG. 105.—THALIA DEMOCRATICA, SOLITARY FORM, ORAL MUSCLES j ^_„„„J -^ nt OF THE RIGHT SIDE, VIEWED FROM WITHIN. FROM STREIFF &™ SCCOnd Sphincters Of (1908). the upper lip are more delicate. They are united at their base, and distally make something of a network, seeming to correspond to the second sphincter of the upper atrial lip of Iasis zonaria. The first, admarginal, sphincter, which in Iasis is continuous through both atrial lips, is wanting in Thalia. The gut forms an elongated loop (fig. 104, B), being bent upon itself in a vertical plane, much as in Traustedtia (pi. 14). The two limbs of the loop are closely appressed in some i
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