82 



(JEODIA ATAXASTRA. 



anatriaene- and mesoproclade-cladomes were found further down in the choano- 

 some. Most of the mesoproclades seen protruded 800 /i-l mm. beyond the 

 surface. The small remnants of spicule-fur observed consisted nearly entirely 

 of the distal parts of such spicules (Plate 44, fig. 27b). 



In the interior no minute rhabds are observed; in the distal part of the 

 choanosome and in the inner and middle (sterraster-armour) layers of the cortex, 

 on the other hand, such spicules, for the most part situated radially, occur in 

 considerable numbers. Where the dermal layer is better preserved, particularly 

 over the entrances to the radial cortical canals, large numbers of minute rhabds 

 are observed. They are here situated radially, their distal ends protruding a 

 little beyond the surface. These minute dermal rhabds are arranged in groups, 

 those of the same group being either parallel or diverging distally tuft-fashion. 

 Most of these spicules are amphiox, a few amphistrongyle or style. Minute 

 amphistrongyles and styles are relatively much more numerous in var. latana 

 than in var. angustana. In var. angustana a few minute dermal anaclades are 

 intermingled with these minute dermal rhabds. 



In the interior of the choanosome a few sterrasters and large, few-rayed 

 oxyasters occur. The latter are situated in the canal-walls. In the distal part 

 of the choanosome and the inner layer of the cortex oxysphaerasters, acanth- 

 tylasters, small strongylosphaerasters, and ataxasters are met with. The 

 middle layer of the cortex is occupied by dense masses of sterrasters. It also 

 contains the parts of the rhabdomes of the fur-spicules which traverse it, the 

 minute rhabds mentioned above, and small strongylosphaerasters and ataxasters. 

 In the dermal membrane a thin but dense layer, composed of small strongylo- 

 sphaerasters and ataxasters is observed. The strongylosphaerasters are much 

 more numerous than the ataxasters. 



The large choanosomal am.phioxes (Plate 43, figs. 23d, 27d) are usually slightly 

 curved, fairly isoactine, and gradually attenuated to sharp points, much more 

 rarely blunt at one or at both ends. The last-named forms are relatively much 

 more frequent in var. latana than in var. angustana. The measurements of 

 three amphioxes, two isoactine and one anisoactine, given in the subjoined table, 

 indicate the degree of attenuation towards the ends. 



