SIBOGLINUM CONCINNUM 287 



superficial transverse wrinkles and folds (Fig. DD133i?). The rings are 

 greyish or, in transmitted light, brownish. They are more or less regular and 

 their length varies between a third and a half of the diameter of the tube 

 (Fig. DD133C, D). One often encounters irregularities in their development. 

 The longest tube I have seen was 200 mm long. The diameter of the tube 

 near the front end varies from 0-25 to 0-33 mm. 



S. subligatum belongs to the group of species typified by S. taeniaphorum, 

 which form a discrete and increasing group within the genus. The species 

 are characterized by the following features: 



1. Longitudinal glandular ribbons of the mesosoma and anterior part of 

 the trunk; 



2. A pair of triangular ventral glandular areas in front of the bridle; 



3. Two or three girdles lying close together; 



4. The very small size of the anterior group of teeth on the toothed 

 platelets; 



5. The characteristic whitish tube which for the most part is ringed and 

 thick-walled. 



Besides S. taeniaphorum and S. subligatum this group of species includes 

 S. atlanticum, S. concinnum sp. nov., S. lacteum sp. nov., S. elongatum sp. 

 nov. and S. arabicum sp. nov. Exceptionally great resemblances link S. 

 subligatum with the last of these species, which also lacks pinnules. It is 

 distinguished from S. arabicum, however, by the very clear boundary be- 

 tween the protosoma and mesosoma, the continuity and breadth of the 

 glandular ribbons of the mesosoma, and in particular by the stalk-like waist 

 between the fore-part of the body and the trunk, and also by a series of minor 

 features, such as the size of the toothed platelets, the strong development of 

 the epidermal glands of the trunk and some features of the tube. 



Material: 75 tubes with animals (some fragmentary) and many empty 

 tubes, besides 18 tubes with embryos. 



Locality: Vityaz? station 4652 (31st cruise): the western part of the Indian 

 Ocean to the north of the Cargados Carajos Islands (North of Mauritius) 

 on the western slopes of the Nazareth Bank (c. 18°S 60°E). 



Depth: 1740 m.] 



[31. Siboglinum concinnum sp. nov. Ivanov (Fig. EE133) 



In March 1960, while working on an oceanographical expedition on board 

 R.V. Vityaz\ a little off the East African coast, I found one small white 

 ringed tube. In it was a well-preserved front half of the body of a nondescript 



