/. Starkie Gardner — On the Gault Aporrhdidce. 291 



comminuted pumice, proving the lava, from the trituration of which 

 it proceeded, to have been a highly siliceous trachyte. The apparent 

 absence of ash-clouds from the first-named eruptions may perhaps 

 be attributed to the winds prevailing at the time having driven them 

 in the direction contrary to the observer's line of sight, since it is 

 difficult to suppose that continuous explosions of fragmentary lava, 

 at first liquid, but soon of course consolidated in that cold climate, 

 should not, by the repeated hurtling together and trituration of their 

 substances in the air, as they rose and fell successively, have produced 

 considerable clouds of ash, that is, of comminuted lava or pumice. 



We shall look with some interest to the further and more detailed 

 accounts of these Icelandic eruptions, which may be expected to 

 arrive before long ; especially as several English explorers, and par- 

 ticularly Mr. Watts, who last year penetrated the Vatnajokull, which 

 no one, it is supposed, not even a native Icelander, had ever trodden, 

 are at present re-exploring the same interesting district. 



II. — On the Gault Aporrha'i'd^. 

 By J. Starkib Gardner, F.G. S. 

 (PLATE VII.). 



{Continued from page 203.) 



Group 4 {continued). — Apoerhais Parkinsoni, var. Cunningtoni, 

 Gardner. PL VII. Fig. 1. 



Shell elongated, spire composed of many convex whorls, which are 

 very finely striated, 2 or 3 of the striae being very distinct and wide 

 apart in front of the sutures. The last 2 whorls have 10 or 11 and 

 the other whorls have 14 or 16 well-marked ribs, with occasional var- 

 ices. On the last whorl there is a slight angularity in place of keel. 

 The wing exactly resembles that of A. Parkinsoni, and in this may 

 be distinguished from that of A. Mantelli. The anterior canal is 

 moderately long. 



The form here described is intermediate in character between A. 

 Parkinsoni and A. Mantelli, differing in the number and development 

 of the ribs from the former and in the shape of the wing from the 

 latter. The specimen was obtained by Mr. Cunnington from the 

 Upper Greensand at Devizes, and is now in the British Museum. 



The next species described cannot be placed satisfactorily with 

 any of the groups just indicated. Prom the species being founded on 

 an unique shell, it is just possible that it may be an abnormal 

 variety. 



Aporrhais macrostoma, Sowerby. PL VII. Fig. 2. 

 Description. — Shell elongated, spire composed probably of '7 or 8 

 convex whorls. Each whorl has two principal keels, which are pro- 

 longed on the last into ridge-like supports to the wing. The first 

 whorl remaining on the specimen now described (probably the 3rd 

 or 4th from the apex) is strongly ribbed transversely, and the two 

 carinas are very salient ; the next whorl has only traces of the ribbing 

 left in the form of widely separated tuberculations on the carinas. On 



