124 GEODIA AGASSIZII. 



DIMENSIONS OF THE ORTHOPLAGIOTRIAENES OF GEODIA AGASSIZII. 





2886 



2887 



2978 



3088 



3168 



4193 



4199 



4228 



4551 



From 

 all Sta- 

 tions 



4228 



Rhabd- 

 ome 



length 



of apparent- 

 ly full-grown 

 spicules, mm. 



2— 

 3.2 



1,9- 

 3.1 



2.1- 

 4.2 



2.5- 

 3.7 



2.4- 

 4 



2.9- 

 3.8 



2.8- 

 3.4 



15- 

 2.8 



2.3- 

 3 3 



1 .5- 

 4,2 



2- 

 3.5 



average of the 

 three largest 

 dimensions, 

 mm. 



3.1 



3 1 



4 



3.6 



3 9 



3 6 



3.7 



2 5 



3 



3 39 



3,3 



thick- 

 ness 



of apparent- 

 ly full-grown 

 spicules, ]i 



73- 

 110 



90- 

 110 



145 



80- 

 120 



90- 

 137 



65- 

 95 



70- 

 103 



so- 

 los 



90- 

 150 



65- 

 150 



50- 

 100 



average of the 

 three largest 

 dimensions, /j 



103 



110 



139 



120 



132 



92 



102 



98 



143 



115 44 



90 



Clades 



length 



of apparent- 

 ly full-grown 

 spicules, 11 



270- 

 500 



250- 

 530 



270- 

 520 



270- 

 530 



320- 

 520 



400- 

 550 



320- 

 560 



440- 

 520 



240- 

 450 



240- 

 560 



300- 

 500 



average of the 

 three largest 

 dimensions, ii 



467 



507 



483 



493 



483 



520 



540 



497 



428 



490 89 



490 



angle 



of apparent- 

 ly full-grown 

 spicules, ° 



94- 

 104 



95- 

 109 



92- 

 104 



73- 

 110 



83- 

 100 



94- 

 117 



90- 

 105 



95- 

 100 



86- 

 105 



73- 

 117 



88- 

 108 



average, ° 



100 



102 



96 



99 



92 



104 



98 



97 



96 



98,2 



97 



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 // 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 below the rounded end. They are 78-300 p. 

 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 



