288 



BUSH 



or 7) serrations, the lowest large and fang-like. As all of these char- 

 acters differ greatly from those of Placostegus tridentatus^ the type 

 of the genus Placostegus (p. 221), the new genus Protoplacostegus 

 is therefore proposed for Mcintosh's species. 



Genus Spirorbis Daudin. (See p. 247.) 



On several specimens of Margaritifera^ recently received from 

 Beirut, Syria, are numerous tubes of three species of Spirorbis, 

 One sinistral form is moderately large, regularly coiled, the surface 

 more or less roughened by irregular concentric growth lines but with 

 no distinct sculpture. The animals examined have a calcareous plate 

 in the operculum, shallow, oblique, cup-shaped with broad, short base, 

 with a conspicuous spine at the back, not differing from that figured 

 by Marion and Bobretzky (1875) for Spirorbis cornuarietis of Phil- 

 ippi. The collar setae have coarsely serrate tapered blades with coarse 

 fin-like bases. On comparing this with the figure given by Philippi 

 (1844) there was found a decided difference in the size and position of 

 the basal spine, that of Philippi's species being figured as on the front 

 just below the deepest part of the cup, while in the present form and 

 in that figured by Marion and Bobretzky the spine is at the back and 

 rudder-like in form. Philippi also described his species as having the 

 tube concentrically striated, so that there may be some confusion in 

 the identification of the species, and that described and figured by Marion 

 and Bobretzky may be distinct. If, however, upon further study it 

 proves to be the same as Philippi's, this species is erroneously placed 

 in the table on p. 260 and should be transferred to the first group with 

 species whose tubes are unsculptured, the growth lines not being 

 treated as such. 



Another animal has the calcareous plate of the operculum composed 

 of two distinct pieces. The end one is a similar, oblique, shallow cup 

 with spreading base, which has an elongated, narrow, median portion 

 thickened along its back, forming three conspicuous serrations ; pos- 

 terior to and in front of the base of this end piece is a large concavo- 

 convex, shield-shaped one which is entirely detached from it and is 

 very unlike the comparatively thin, firm, elongated, shield-shaped pro- 

 tection wall found in the opercula which form brood-pouches. The 

 collar setae are coarsely serrate with basal fin. The tube is sinistral, 

 of good size, with the surface roughened by faint spiral threads and 

 irregular growth lines. Smaller dextral tubes have the surface orna- 

 mented with definite spiral threads crossed by distinct concentric lines. 

 The animal has but a simple calcareous disk in the operculum and the 



