80 THE VOYAGE OF H.M.S. CHALLENGER. 



arranged in rather distant and irregular longitudinal rows of spirals. The stigmata are 

 huge, they are curved in the spirals and more or less linear between. Delicate radiating 

 tubes are frequently present. 



The Dorsal Lamina is a plain narrow membrane. 



The Tentacles are branched, but not large ; they' are numerous and of many sizes, 

 arranged indefinitely. 



The Dorsal Tubercle is very simple, and is tubular ; it has a wide funnel-shaped 

 aperture anteriorly, which rapidly narrows as it runs backwards and becomes lost in the 

 neural gland. The peritubercular area is large and triangular. 



This species has a curious external form, the posterior end, contrary to the usual rule, 

 being narrow and pointed, while the anterior is broad and flat (PI. VI. fig. 1). 



The mantle is not very muscular, and over the greater part of its area the fibres are 

 arranged, chiefly three to six or more together, in short fusiform clumps which taper 

 suddenly at the two extremities and end in long delicate filaments. 



The chief characteristic feature in the branchial sac (PI. VI. fig. 2) is the structure of 

 the folds. These are very simple and consist merely of two or three additional internal 

 longitudinal bars attached to each normal one by short transverse ducts, like the 

 connecting ducts from the transverse vessels. These ducts are placed in the same line 

 with the horizontal membranes, and thus seem to indicate the position of the transverse 

 vessels (PI. VI. fig. 2, h.m.). In some of the folds there are twice as many ducts 

 between the second and third internal longitudinal bar as between the first and second, 

 so that if, for example, the first and second bars were connected by a transverse duct at 

 every millimetre the second and third bars would be connected by ducts at every 

 millimetre and every half millimetre. 



There are seven folds on the right side of the sac and only six on the left, but, as 

 the collection contains only one specimen of the species, this may be an individual 

 abnormality. The stigmata are large and in some places are arranged in spirals, forming 

 shallow infundibula. Between the spirals the stigmata are generally linear, and form 

 irregular transverse rows. They are frecpiently crossed by narrow tubes (PI. VI. fig. 2). 



The dorsal tubercle is extremely interesting. It is in the simplest possible form, 

 being merely the widened aperture of the duct from the neural gland. This duct may 

 be seen distinctly (PL VI. fig. 3) running anteriorly and swelling out to form the large 

 funnel-shaped aperture. It is placed near the anterior end of the large and deep 

 triangular peritubercular area, which extends so far posteriorly as to include in its area 

 the greater part of the neural mass (PL VI. fig. 3, n.). 



A single specimen of this species w r as dredged off the coast of Buenos Ayres, South 

 America, at Station 320; February 14, 1876 ; kit, 37° 17' S., long. 53° 52' W. ; depth, 

 600 fathoms ; bottom temperature, 2°'7 C. ; bottom, hard ground. 



