552 DESCRIPTIONS OF ANNELIDS. 



There are eight specimens of this species in the collect iou, four from 

 St. Thomas and four from Cura9ao. The St. Thomas specimens are 

 somewhat darker and smaller than those from Cura9ao. The operculum 

 of a small specimen from St. Thomas is nearly circular (fig. 38). A 

 slightly larger specimen shows a ridge running back from the horns to 

 the center of the disk, as is the case with specimens of the same size 

 from Cura9ao. 



Figs. 41 and 42 show an operculum of a large specimen from Cura9ao, 

 in which the ridge runs back to the posterior edge of the disk and is 

 elevated, having four short horus projecting at the end. 



The branchiae of the large specimens are eight-spiral ; those of the 

 small, five-spiral. 



The collar-setai are of two varieties (figs. 43 and 44). The points of 

 setse represented by fig. 43 were invariably broken. The figure shows 

 the point restored by i>roducing the outlines to an intersection beyond 

 the break. 



The thoracic uucini (fig. 45) have from sixteen to eighteen teeth ; the 

 abdominal (fig. 46), from ten to thirteen. 



The collars of all the specimens are of a deep blue ; the branchiae are 

 rose-red, variegated with flesh-color. 



As is well known, this species lives in tubes formed in coral. The 

 mouths of the tubes are made smooth by a secretion of carbonate of 

 lime of a light-purple tinge. A single curved spine of the same sub- 

 stance projects over the entrance of the tube (fig. 40). This is undoubt- 

 edly secreted by the worm. 



The largest specimen is about TS'""' in length and 9™™ in breadth ; 

 the smallest about 40™™ in length, and 5™™ in breadth. 



Colors and sizes taken from specimens in strong alcohol. 



Coral reefs; shallow water (961-964). 



Spirobranchus incrassatus (Kroyer) Morch. 

 (Plate xxiii. fig. 48. Plate xxiv, fig. 49.) 



Cymospira incraasata Kroyer, Mus. Reg. 



Cyviospira incrassata Quatrefages, Hist. Nat. ties Anu., t. ii, p. 545. 



Spirobranchus incrassatus Miirch, Rev. Grit. Serp., p. 59, pi. xi, ligs. 21-23. 



A single specimen of this species was placed in the collection by a 

 member of the Mexican Geographical Commission. It agrees quite well 

 with Month's description and figures, except that the unpaired horn 

 arises from the operculum (fig. 49) at the same angle as the large pair, 

 and all are much nearer the center. The true outline of the opercuhim 

 is shown in fig. 4S. The branchiae are eight-spiral. 



It is probable that a large series of specimens would show this to be 

 a variety of S. (jiganteus^ or even a form due to age. The species was 

 described originally from the Pacific Ocean. 



The long collar-setoe are the same in size and shape as those figured 

 from *S'. giganteus. It was impossible to com^jare the small collar-setaj. 



