TETRERES MITRATA. 9 



found in the tissues in this region in Sabellaria spinulosa may be the homologues of these 

 hooks. In the hollow in front of the hooks a series of symmetrical folds converge to the 

 margin of the fork in front of the mouth, whilst the groove behind has transverse or 

 curved furrows and much brown pigment. 



The ventral face of each coronal lobe is slightly turned inward and densely covered 

 with proportionally small tentacles, which in their firm attachment and general aspect 

 resemble those of Fhoronis rather than Sabellaria. These are attached directly to the 

 surface of the lobes, and thus differ from the arrangement in Sabellaria. In some they 

 form oblique rows slanting from behind forward and outward at their commencement on 

 the external ridge posteriorly. After a short distance they spread to the inner border 

 and thus cover the ventral surface with the exception of a belt internally, but the rows 

 are not evident either on the inner border or on the outer after the middle. Those in 

 front and internally do not present the same regularity in the rows ; indeed, in one they 

 were irregular. Both show a bare longitudinal stripe along the centre — that is, between 

 the outer and inner series — till near the tip. The tentacles are richly ciliated along one 

 surface, show an afferent and an efferent vessel, and are coloured of a deep brown. The 

 great length of the " peristomial " lobes and the extended surface covered by the tentacles 

 indicate a special function. 



The mouth opens at the posterior end of the great lobes and behind the tentacles. 

 In contraction it forms a puckered longitudinal slit with two overlapping flaps in front, 

 whilst in partial dilatation it has a series of separate folds or " cushions " externally, and 

 internally the posterior folds of the hood ; whilst in front the hood is folded forward in the 

 middle line like an epistome, and forms a collar at each side before joining the posterior 

 folds. The whole would thus form a characteristic funnel leading to the mouth. The 

 hood is fixed all round a little behind its margin. Mr. Arnold Watson, who at first 

 thought that the frilled membrane which runs from the extremity of each peristomial lobe 

 was an extension from the sides of the prostomium, has by careful examination of the 

 living forms now (1916) found that though this membrane is in its lowest (most posterior) 

 part united with the edge of the prostomium, yet it is distinctly and deeply separated at 

 its free upper edge. Its origin, therefore, is the same as the outer edge of the channel, 

 and both should be regarded as peristomial. On the dorsal aspect of the hood are 

 the two long tentacles which have a smooth dorsal edge and a deeply grooved ventral 

 surface with frilled margins — probably ciliated in life — and they occupy a smooth and 

 pigmented area of the pillars to the inner edge of the outer tentacles. 



Besides the two lateral tentacles (palps of some) a median subulate one springs from 

 a slightly elevated and antero-posteriorly elongated base somewhat in front of the lateral. 

 This may have a function in connection with the forward frill of the hood. The parts 

 thus differ considerably from those of Sabellaria, especially in the great development of the 

 hood. The lobes overlapping each other and the hood present evidences of transverse 

 striation, so that the function is special. Externally is a large lanceolate lobe (Dr. Allen's 

 neuropodial cirrus of the first segment) connected at its base by a frill with a small 

 elevation bearing bristles (ventral, Allen), as in Sabellaria. 



Allen thinks the two tentacles have the same structure as those of the Spionidge and 

 Disomidae, being D-shaped in section with the grooved surface bordered by a crenate 



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