GEODIA AGASSIZII. 139 



branched are more numerous than the orthoplagiotriaenes with simple and 

 regular clades. In the others all, or nearly all, orthoplagiotriaenes have simple 

 and regular clades, orthoplagiotriaenes with clades like those of the majority 

 of E, F, and G being very rare or absent altogether. In the clades of the ana- 

 triaenes of G and H the straight distal part is considerably longer than in those 

 of the others. In E and H anatriaenes with clades unequal in length or position 

 have been met with. In some of the anaclades of E one clade is absent alto- 

 gether, these spicules appearing as anadiaenes. Oxyasters over 26 fi in diameter 

 with irregularly arranged rays have been found only in H. The small strongylo- 

 sphaerasters of C and F have on an average smaller centra than those of the 

 others. In A and E the large oxysphaerasters are much more numerous than 

 in the others. 



In dimension the spicules of the lots from the different stations differ more 

 or less. To obtain a base for studying these differences the sets of measure- 

 ments of the fifteen spicule-dimensions obtainable with the greatest accuracy 

 of each of the nine lots of adult specimens from the nine stations, were selected 

 for further study. These dimensions are: — the diameter of the oxyasters; 

 the length and breadth of the sterrasters ; the length and thickness of the large 

 choanosomal amphioxes, the small dermal amphioxes, and the rhabdomes of the 

 orthoplagiotriaenes; the thickness of the rhabdomes of the anatriaenes and 

 mesoprotriaenes; the length of the clades of the orthoplagiotriaenes, anatriaenes, 

 and mesoprotriaenes; and the length of the epirhabds of the mesoprotriaenes. 

 Of each of these (15 X 9 =) 135 sets of measurements the largest alone were taken 

 into account. Of three, the length and thickness of the small dermal amphioxes 

 and the diameter of the large oxyasters, the largest dimension observed in each 

 lot was taken by itself. Of the twelve other dimensions averages of the three 

 largest dimensions measured were taken. These single maxima and maximum 

 averages of three of the fifteen spicule-dimensions taken into account in the nine 

 lots are given in IV of the subjoined table. From these maximum averages 

 (maxima) the general averages (means) were taken. These general maximum 

 averages (means) are given in II of the table. The deviation of the average 

 maximum (maximum) of each of the fifteen dimensions of each of the nine lots 

 (IV) from the mean (general maximum average, II) of the same dimension was 

 ascertained by subtraction. These (135) deviations are given in V of the table. 

 Referring as they do to spicule-dimensions of very different size the numbers 

 giving these deviations are not commensurate and directly comparable with 

 each other. To obtain numbers expressing these deviations from the general 



