I arinal latus elongated pentagonal, narrow, with the umbo about in the centrum 

 of di htly projecting outwaï 



arina small; solid, pyramidal, standing oul beyond the surface of the carina. 

 Peduncle about half the length of the capitulum, rather narrow, narrowest aboul the 

 middle of its length; surface with minute chitinous scales standin ome distance from one 



ther. In one of the membram .1 specimens of Station 17 the length of the peduncle 



is more than half the length of the capitulum. 



Si. 1 Length of the capitulum 0,1 mm., of the whole animal 13 mm. in the specimen 

 Station 285; in the largest specimen hom Station 17 1, the corresponding dimensions are 

 .n.1 1 3,8 mm. 



< omplemental males. Two complemental mal'-, were observed in one <>l the 



mens from Station 47 attached to tin- surface ol that part ol the sac or mande of the 



hermaphrodite animal which unites the inferior halves of the two scuta. These males are relatively 



. the longest diameter of the body being <>.ei mm. Their shape is elongated oval and the 



is divided into a larger capitular part and a very short peduncle. The capitulum has six 



valves: 2 scuta. 2 terga, 1 carina and 1 very large rostrum. Fig. 3 of PI. YII has heen drawn 



from the male of this species; it has a great resemhlance to the male of Sc. Peroni and, no 



doubt, that of several other shallow-water species. 



This species was collected by II.M.S. "Siboga" at two Stations, viz. at: 



47. April u, 1 19. Entrance to Bay of Bima (Sumbawa). Depth 296 m. Hottom: fine 



sand with mud (coral). Two specimens. One of tliem was attached to .1 small 



k, t'> which a piece of coral was also attached. 



Stat. 285. January [8, [900. Lat. 8° 39'.! S., Long. i27°4'.4 E. Depth 34 m. On the limit betwecn 



mud and coral, Lithothamnion. (Anchorage south-coast of Timor). One specimen. 



1 (bservations. The present species coines nearest to Sc. Peroni of the known species, 

 e. g. in the number of valves, the shape of the carina and the form (nol the size) of the tergum. 

 It differs from it by the absence of the fine spines which cover the membrane in Sc. Peroni, 

 by the valves not being separated by rather wide interspaces of membrane and in the third 

 place by the shape of the latera. 



At first I considered the specimen from Station 285 (PI. YII, 1'i^. 2) without a distinct 



membrane as being different from the specimens from Station 47 1 ' (PI. Y, fig. 151. which are 



covered with a very conspicuous membrane. Looking at the shape of the capitulum and at the 



form of the different valves more closely, 1 became convinced, however, that there was no 



reason to consider them as specifically distinct. It is truc that they were taken at very different 



depths; l.ut other species also range over depths of rather great difference. Thus, for example, 



ulgare Leach observed in very shallow water and also at a depth of 07 m. For this 



I 1 1 has described a very characteristic case of polymorphism, corresponding in many 



to what I found in Sc. umus, viz. that specimens of different localities 'and depths 



in the development of the membrane covering the valves, of the interspai 



■ dves, as also in the -rade of calcification, the hairiness of the membrane etc. 



■ lies \ii hives du Muséum. 1\ IV, i 



