34 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



and 37. In Fig. 44, which represents the bell margin and velarium of 

 Tripedalia arranged as if the velarium were vertical and pendant from 

 the margin (instead of suspended by the frenulum so as to be at right 

 angles to the vertical plane), the connecting lamella is shown as a dotted 

 line (vie) dotted because it does not come to the surface joining the 

 lamella of the niche with that of the margin (vim). 



The same figure (No. 44) shows a characteristic difference between 

 the marginal lamella of Tripedalia and that of Charybdea. While in 

 Charybdea, as Glaus points out, the marginal lamella keeps at one level, 

 just a little above the bell margin, all the way round (except where dis- 

 turbed by the special modifications of the tentacles and the sensory 

 clubs), and never descends into the velarium, in Tripedalia on the other 

 hand it describes a sinuous course, following the outlines of the mar- 

 ginal pockets, as is indicated in the figure by the light parallel line vim. 

 The course as it would be seen in a surface view is obscured just at each 

 side of the interradius by the overhanging of the bases of the two lateral 

 pedalia. This is why the lamella is not indicated at these points in the 

 diagram. The course is seen to lie almost wholly on the velarium, that 

 is, in the figure below the line which represents the bell margin proper, 

 the line at which the angle comes when the velarium is in its normal 

 position, horizontal to the vertical side of the bell. 



In this sinuous course of the marginal lamella we have another point 

 of resemblance between Tripedalia and the Chirodropidas. H. V. Wilson 

 worked it out in his sections of Chiro psalm us, and the reconstruction 

 which I have given in the figure under discussion is in all essentials 

 similar to his for Chiropsalmus. The differences lie only in the fact that 

 Chiropsalmus has more velar canals, and that the chief marginal pocket 

 in each quadrant is not forked peripherally, as is that of Tripedalia (mp), 

 but presents its distal margin parallel to the edge of the velarium. The 

 two smaller marginal pockets in the perradii (mp') are on identically the 

 same plan in both. 



Tripedalia, having three tentacles joining the umbrella in each inter- 

 radius, shows a disturbance of the course of the marginal lamella in 

 these regions by just so much the more complicated than in Charybdea. 

 The plan, however, is exactly the same. The lamella is pushed upwards 

 from the margin by each of the bases of the three pedalia just as is done 

 by the base of the single pedalium of Charybdea. Fig. 29 shows the 

 lamella in the same relation to the canal of the central tentacle (ci) that 

 it has in the similar sections of Charybdea (Figs. 16 and 43); and in 



