TETRAXONIDA. 43 



the shaft and downwards from the dental bridge, both lamellae Ijeing nearly on the 

 same plane and nearly meeting, the lamellae sometimes with basal tubercles. 

 Developmental forms in shape of thin oval linear bodies, the oval at first not being 

 complete. 



The unique specimen representing the new genus and species is 12' 5 cm. long and 

 1 cm. in breadth at the centre. The body attenuates to fine ends, and apparently 

 has not been attached to anything. 



The remarkable canonochelae recall to mind the sphcrancorae of Meloiiaaclwra, 

 but the latter spicules have three pairs of fused teeth. 



The canonochelae are scattered about in the choanosome in considerable numbers. 

 The shape may be compared with an oval basin with the l)ottom cut out, and with two 

 semi-ck'cular lids or lamellae passing horizontally from the upper edge of the basin, 

 so as to nearly meet ; further it is necessary to imagine such a basin turned up on 

 its side. 



The earliest developmental forms have an elongated C shape ; then the open Q 

 becomes a closed oval ; by this time the falx at each end is perceptible, and the 

 beginnings of the lamellae appear. A further change leads to a marked asymmetry, 

 the thin oval ring becoming a broad band by widening in a direction away from the 

 edges whence the lamellae arise. If the widening of the band were to continue the 

 growing edges would meet and a sort of lateral dome would result, but growth does 

 not go so far as this. 



It is often difficult to make out the real form of a transparent body, with its lines, 

 curves, lamellae, &c., crossing each other in various directions and altering their 

 appearance with the slightest shifting of position. In the present instance the figures 

 will show the remarkable variations in form corresponding to change in position, 

 and it was only after a very prolonged examination that the real shape became 

 apparent, a result finally due to IMr. Highley's ingenuity in devising a medium of 

 suitable consistency in which the spicules could be made to slowly rotate on their 

 long and short axes. Fig. 5 f is the position in which, in spicule preparations, the 

 spicules commonly lie, viz., on the detruncated bottom of the basin and with the 

 lamellar edges uppermost. Fig. 5 h, which resembles the Diatom Amphora, shows 

 the aspect when the shaft portion or the dental portion of the band is uppermost and 

 vie'yed in its breadth ; the axial canal which traverses the shaft and part of the dental 

 bridge is best seen in this aspect. When a spicule in this position continues to rotate 

 a little more we see either the lamellae along one side or the free growing edges of the 

 band on the other. Fig. 5 g shows the growing edge of the dental bridge nearly 

 meeting the edge of the shaft. Fig. 5 k shows half of a spicule broken across, with 

 the axial canal (which forms nearly a complete circuit) exposed at each lower corner of 

 the figure. Lastly an end view is seen in fig. 5 1. 



The specimen was dredged near Winter Quarters at No. iO hole, 130 fnis. 



