124 GEODIA AGASSIZII. 



DIMENSIONS OF THE OUTHOPLAGIOTRIAENES OF GEODIA AGASSIZII. 



The mesorthotriaenes (Plate 26, fig. 1; Plate 29, fig. 7; Plate 34, fig. 16) are 

 very rare and have been found only in the adult specimens from Stations 2978, 

 4199, and 4228, and the young specimen from Station 4228. They consist of a 

 style-like shaft, from which three clades arise. The shaft is conical, 1.8-3 mm. 

 long and 78-164 /i thick at the rounded end. It usually tapers to a simple point 

 at the other end. In one of these spicules, however, the thin end of the shaft 

 was bifid, terminating in two points, lying close together. The three clades 

 form a verticil situated 150-280 jx below the rounded end. They are 78-300 ft 

 long. Their basal part is directed obliquely downward towards the pointed end 

 of the shaft. Distally they curve round towards its rounded end, either uni- 

 formly, or abruptly. It is not quite easy to say which of the two parts of the 

 shaft on either side of the clade-verticil is to be considered as the rhabdome and 

 which as the epirhabd. The fact that the pointed part is very much longer than 



