102 FESTSKRIFT FÖR LILLJEBORG 



length. Tin- arms are connected by a short interbrachial web at their bases. This 

 web is best developed between the third and fourth pairs, where it extends along 

 half the length of the arms. The arms of the fourth or ventral pair are completely 

 separated from each other. The same seems to be the case with Spirilla peronii 

 according to Huxley's figure, and 5. australis according to Owen 1 . The Blake- 

 specimen however is different, and appears to have a web between the ventral arms 

 at least according to the figure reproduced in the Challenger-report pi. II fig. i. 

 Thus the West-Indian form differs from all others 1 ', if correctly reproduced. 



The exterior surface of the arms is rounded, hardly keeled, except a little 

 in the third pair. The oral, or internal surface, is flattened, or a little concave, and 

 carries the suckers. These are so densely and irregularly crowded that hardly any 

 rows can be distinguished. In the middle of the arms there seem to be six longitu- 

 dinal rows, but in other places only four. The cups or suckers are pedunculated, 

 but as Pelseneer remarks (1. c. p. 5), the peduncle is not inserted in the axis of the 

 sucker, but laterally. In the peduncle external a single external layer of fine circular 

 fibres can be distinguished, and within it some stronger, longitudinal ones, which can 

 be followed with the eye to the central papilla where they insert themselves (Fig. 10). 



Th<- "horny" armature (Pig. 10 & n) in each sucker is strongly developed. 

 It is composed of an outer concave but shallow "collar" and an interior globular 

 section without bottom. The aperture to the interior cavity of the sucker is armed 

 with 14 to 16 strong teeth of nearly equal size. The exterior margin of the collar, 

 on the other hand, is provided with smaller toothlike thickenings which protrude a 

 little so that the margin looks feebly crenulated. Between these marginal teeth and 

 the big teeth round the aperture we find two concentric, interior circular rows of 

 large tubercles and an exterior row of smaller ones; the latter is not always con- 

 spicuous all round. The large tubercles consist of a lower basal part and a rounded 

 wart on the top; the latter, especially in the innermost row, may have the shape 

 and size of a tooth so that these tubercles form a sort of accessory teeth. The col- 

 larlike part of the armature is thus quite different to that of Spirilla peronii, to judge 

 at hast from Huxley's fig. 9& 10, PI. VI, 1. c. in which no tubercles are visible, 

 except as tiny granules; the teeth round the opening are strongly developed only on 

 one side and they appear more pointed. 



The inner or globular section of the armature represents the real acetabu- 

 lum. It acts by means of the retraction of the "central papilla" brought about by 

 the contraction of the longitudinal muscles of the peduncle. When, on the other 



' <'. ml. Ann. Mag. I. c. pi. I. figs. 5 & 7. 

 - Conf. the note above. 



