OF CONCHOLOGY. 311 



Ancylus textilis, n. sp. PL 17, figs. 9, 10, 11. 



Shell suboval, rather depressed, thin, horhy-brown-colored, 



minutely decussate ; apex recurved towards the right margin, 



which it approaches rather closely. A large example measures 

 in length 6 mill., in breadth 4 mill. 



This Ancylus is near to A. culieoides, d'Orb., from Guayaquil, 

 but most of my examples are of more oval figure, and the apex 

 is generally more decidedly recurved. There is considerable 

 variation in the proportions of the shell, some examples resem- 

 bling A. coneenfricus, d'Orb. Small specimens are liable to a 

 peculiar monstrosity, consisting in the development of a plate, 

 joining more or less extensively the margins of the aperture. 

 This plate is usually slightly convex, and when, as in some cases, 

 only a small opening is left for the exit of the animal, the edges 

 of the opening are a little produced and everted. Fig. 11 shows 

 this form ; Fig. 10 shows the aperture partly closed ; Fig. 9 is 

 the upper surface. 



Chatham and Santa Cruz Rivers, Trinidad. 



Bland has suggested to me that Ancylus textilis is a Gfund- 

 lachia. In all the largest examples which I have seen, there is 

 no trace of the septum commonly found in young shells, and 

 occasionally present in older or medium-sized individuals, such 

 as those of which I give figures. A number of young specimens, 

 developed in my aquarium, showed the septum, but many of 

 equal size had no sign of it. I should say, then, that my species 

 is an Ancylus, which has sometimes, in its young state, the pecu- 

 liar character of Gu7idlachia, but rarely so in its older state. 



