Brooks.] 382 [May 18, 



The conchiolin tube commences as a closed sac fitting into the 

 sheath of the apical chamber. It extends unchanged in thickness 

 through the first funnel. From the second to the fourth septum 

 the tubes are much drawn out and attenuated so as to be transpar- 

 ent at the points where they pass through the funnels. At the 

 fifth or some subsequent septum, the exact number of which has 

 not been fully ascertained, a change takes place and the tubes no 

 longer pass through the funnels but are disconnected. 



They extend from the posterior inner portion of one funnel to 

 the outer posterior edge of an anterior funnel. The anterior ends 

 of the tubes are often forked and embrace both the outer and inner 

 edges of an anterior funnel. The funnels of the young septa are 

 much longer in comparison to the depth of the chambers than are 

 the funnels of the older septa. The older funnels diminish in length 

 as the chambers increase in size. They are made up of five layers : 



(1) An outer layer formed by the anterior end of a posterior 

 sheath, where it embraces the funnel. 



(2) A darker and denser layer than the outer layer which con- 

 tains more organic matter. 



(3) The shell layer of the funnel proper. 



(4) The dense layer forming the posterior end of an anterior 

 spiculous sheath. 



(5) An inner layer that is extremely short and reduces the open- 

 ing of the funnel at its posterior end. This inner layer shows in 

 section as a semicircle. 



The last two layers are not present in the funnel of the living 

 chamber. 



The formation of the funnels of the young septa will be de- 

 scribed in another paper. 



EXPLANATION OF PLATES. 



Plate 1. A longitudinal section of an older funnel showing the five layers, and 

 portion of the anterior and posterior spiculous sheaths and conchiolin tubes. 

 Plate 2. A diagram explaining Plate 1. 



a. Anterior end of a spiculous sheath where it embraces a funnel. 

 6. The dense layer between the sheath and the shell layer of the funnel. 



c. The shell of the funnel. 



d. The dense end of a posterior sheath before it becomes spiculous. 



e. Dense layer that reduces, the opening of the funnel. 

 /. Anterior portion of a conchiolin tube. 



ax. Posterior end of a sheath showing how it fits into the funnel. 

 fx. Anterior end of a conchiolin tube showing where it joins the posterior end of 

 funnel. 



