GEODIA AGASSIZII. 



119 



from Stations 2886 and 3168 than in those from the other stations, are chiefly 

 met with in the walls of the cortical and subcortical canals (Plate 26, fig. 14) 

 and in the inner layer of the cortex. The large oxyasters are scattered through- 

 out the choanosome, where they chiefly occupy the canal-walls. The sterr- 

 asters occupy the middle layer of the cortex in dense masses (Plate 27, figs, lb, 

 2b; Plate 32, figs. 8a, 11a, 12a). In some specimens, particularly the adult 

 specimen from Station 3168 and the young specimen from Station 4228, a good 

 many sterrasters, chiefly young ones, also occur in the choanosome (Plate 32, 

 figs. 8, 11, 12). A small number of sterroids are usually associated with the 

 sterrasters. 



The large amphioxes (Plate 28, figs. 15, 16a, 17a; Plate 32, figs. 9, 10) are 

 numerous in all the specimens. They are cylindrical in their central part and 

 rather abruptly and not very sharply pointed, sometimes blunt at the ends. 

 They are usually isoactine or slightly anisoactine, a few are strongly anisoactine. 

 In the adult specimens they are 2.3-4.8 mm. long and 60-112 // thick, their 

 general average maximum ^ dimensions being 3.9 mm. X 86.3 /«. In the speci- 

 mens from Station 2886 and the adult specimen from Station 4228 they are 

 smaller, both shorter and thinner, than in those from any of the others. In 

 the specimens from Station 4193 they are very slender, longer than in any and 

 thinner than in most of the others. In the specimens from Station 2978 they 

 are of medium length, but very much thicker than in any of the others. In the 

 young specimen from Station 4228 the large amphioxes are 2.1-3.4 mm. long 

 and 20-66 p. thick, their average maximum dimensions being 3.1 mm. X 57 /<. 

 In the immature specimen described by Lambe these amphioxes measure 1.8- 

 3.4 mm. by 33-47 ft. (See table p. 120.) 



The rare large aynphistrongyles , which have been observed in the young 

 specimen from Station 4228 are somewhat shorter than the large amphioxes, 

 about 55 fj. thick in the middle, and attenuated to about 40 /x at the rounded, 

 somewhat truncate ends. 



The kn^ge, slender, cylindrical shjles (Plate 28, fig. 17b) which have been found 

 in small numbers in all the specimens, with the exception of those from Stations 

 2887, 2978, 4228, and 4551, are 1.5-3.4 mm. long and 60-110 /( thick, gently 

 curved, and only slightly thickened, or not thickened at all, at the rounded end. 



' In all cases these average maxima were obtained as follows: — first the averages of the dimen- 

 sions of the three largest amphioxes of the (adult) specimens from each of the nine stations were taken. 

 From these special maximmn averages (of three), which are given in the subjoined table, the averages 

 were again taken. These latter averages (means) which appear in the subjoined talkie in the column 

 headed "from all stations" are the "general maximum averages." 



