282 MESSES. E. HEEON-ALLEN AND A. EAELAND ON THE 



masked by the secondary shell-matter, but become visible when wetted. The second or 

 turgid type, which occurs abundantly at Stn. 22 and elsewhere, is much larger, the 

 chambers being less inflated and more numerous, ranging up to eight or nine in the 

 final embracing convolution ; sutural lines depressed, but less so than in the compressed 

 tvpe, and filled with the same granular matter radiating from the depressed umbilicus, 

 but to a lesser degree. The retral processes are much more numerous than in the 

 compressed type, and, although rarely visible in the dry shell, come out strongly when 

 wetted. 



The compressed type is evidently to some extent isomorphous with N. scapha (as 

 observed by Fornasini) and the turgid with N. depressula. Both forms represent 

 connecting-links between the two species and P. striato-punctata, as also does P. de- 

 cipiens, though on a different line of development. 



318. Polystomella decipiens, Costa. (Plate 43. figs. 20-22.) (New to Britain.) 



Polystomella decipiens, Costa, 1853, etc., PRN. 1856, p. 220, pi. xix. fig. 13 a, b. 

 „ „ Fornasini, 1897, FIC. p. 17, pi. ii. fig. 12. 



Fornasini, 1899, PF1. p. 646. 



5 Stations. 



This specific name of Costa's, though of no zoological value, has a taxonomical use 

 for recording those extremely pauperate specimens of P. striato-punctata in which the 

 scptation and fossettes are so obscure that specimens are with difficulty separated from 

 Nonionina depressula. It occurs at a few Stns., the best at Stns. 5 and 17. It has, no 

 doubt, been included in many lists under P. striato-punctata. 



319. Polystomella striato-punctata (Fichtel & Moll). 



Nautilus striato-punctatus, Fichtel & Moll, 1798, TM. p. 61, pi. ix. figs, a, b, c. 

 Polystomella striato-punctata, Brady, 1884, FC. p. 733, pi. cix. figs. 22, 23. 



25 Stations. 



Universally distributed, generally very abundant and constant in type, practically 

 the only variation being in the thickness of the shell. The very thick typical form is 

 most general, occurring practically everywhere ; the thinner form (cf. P. poeyana, d'O. 

 1839, FC. p. 55, pi. vi- figs- 25, 26) occurs in lesser numbers at nearly all the Stns. At 

 Stn. 17 a good many distorted and abnormal individuals were found, including one 

 in which the initial spiral was followed by five chambers arranged in a straight line, 

 forming a long crozier-shaped shell. 



320. Polystomella Striato-punctata, var. selseyensis, Heron-Allen & Earland. 

 Polystomella striato-punctata, var. selseyensis, Herou-Allen & Earland, 1908, etc., SB. 1909, p. 695, 



pi. xxi. fig. 2, 1911, p. 448 (table) ; 1914, etc., FKA. 1915, p. 733. 



7 Stations. 



Widely distributed in company with the type, never very abundant, the best at 

 Stns. 4 and 5. 



