DESCRIPTION OF PLATE, 17. 651 



PLATE 17. 



Genera — Platylepas, Tubicinella, and Xenobalanus. 



Fig. 1 a, Platylepas bissexlobata, shell of, viewed from the under side. 



a, rostrum ; B, lateral compartment ; c, carino-lateral com- 

 partment ; e, carina. These letters are placed opposite the 

 inward folds of each compartment forming the midribs. 



1 b, Platylepas bissexlobata, shell of, viewed externally. 

 1 c, „ ,, scutum and tergum, viewed externally 



and separated. 



1 d, „ „ lateral compartment, viewed from the 



inside, showing the inward folded 

 wall or midrib; a', ala; d, radius. 



2 a, Platylepas decorata, shell, viewed externally ; a, rostum ; 



b, lateral compartment ; c, carino-lateral compartment ; 

 e, carina. These letters are placed opposite the inward 

 folds of each compartment. 



2 b, „ ,, minute portion of external surface of 



wall, magnified. 



3 a, Tubicinella trachealis, natural size; p, tubular soft lip leading 



into sack; s, scutum; t, tergum. 

 3 b, Tubicinella trachealis, carino-lateral compartment of a young 

 specimen, natural size ; e, broken summit of wall ; d, ra- 

 dius : the dotted lines, connecting the two figures, show 

 the size and form which this compartment would have 

 attained, if it could have grown without the summit con- 

 stantly breaking away. 



3 c, Tubicinella trachealis, scutum and tergum viewed from • 



within, and connected by layers of thickened membrane ; 

 the scutum is to the left-hand. 



4 a, Xenobalanus globicipitis, enlarged ; b, skin of the porpoise, 



with the shell imbedded ; at c the lower end of the prosoma 

 of the included animal's body is supposed to be seen through. 

 4 b. Xenobalanus globicipitis, shell greatly enlarged, seen from 

 above, with the basal membrane at the bottom ; the 

 peduncle-formed body having been removed. 



a, rostrum, on the inner side of this and the adjoining compart- 



ments, the transversely ribbed sheath can be seen. 



b, lateral compartment. 



c, carino-lateral compartment. 



e, carina ; these compartments are separated by the sutures s $, 

 which run from the top of the shell to the bottom, along the 

 ends of the six rays formed by the adjoining portions of 

 the inwardly folded compartments. 



a, alae, of rectangular shape. 



d, pseudo, or complimentary radii. 



4 c, Xenobalanus globicipitis, small portion of external surface 

 of wall of shell, showing the external lamina, a a, which 

 consists only of narrow ledges (expanding and contracting) 

 on each side of the longitudinal septa, c ; b, the internal 

 lamina. 



