LUDWIGIA LUCYI. 105 



At a diameter of about 2 lines, and at what is about the third whorl, we 

 find the commencement of the ribs, but with no trace even of keel ; at 3 lines the 

 ribs are straight, and sometimes joined on the inner margin, the ventral area is a 

 trifle less rotund, the sides of the whorls are divergent, the aperture as broad as it 

 is high, and less than half the preceding whorl is occluded. At a diameter of just 

 under 5 lines the ribs are slightly recurved, the point of bifurcation is a little 

 further from the inner margin, the sides are the least trifle more compressed; but 

 the other characters are about the same. At a diameter of 7 lines the carina 

 begins to be distinct, the sides of the whorls are more compressed, the height of 

 the aperture being about one-and-a-quarter the breadth, and the inclusion is rather 

 more than one-half the preceding whorl. At a diameter of 14 lines the carina is 

 distinctly and strongly formed, the inner margin has just commenced to be 

 distinct, the sides of the whorls are compressed — the height being one-and-a-half 

 times the breadth — the inclusion is three-fifths the preceding whorl, and the ribs 

 are strongly marked and recurved. At a diameter of about 2\ inches the ribs 

 begin to be less strongly marked, the height of the aperture is twice the breadth, 

 and the inclusion is almost four-fifths of the preceding whorl. 



The large prominent carina separates the type-form of this species from all 

 forms of Ludwigia Murchisonce. Its broad whorls, and narrow, deep umbilicus 

 distinguish it from the coarse-ribbed L. obtusa ; its broad, obscure, widely-separated 

 ribs distinguish it from the narrow-centred L. Bay Hi. The young have much 

 resemblance to L. costosa, but are far thicker. Although in ribbing this species 

 has perhaps more resemblance to L. costosa than to L. Murchisonce, yet I am 

 inclined to think that it is a descendant of the latter rather than the former, on 

 account of its thicker, squarer proportions and more general resemblance in 

 aspect, and also because the series descended from the former are all small species. 



What I must for the present class as a variety of this species is depicted on 

 Plate XXI, figs. 10 and 11, and is especially noticeable. It differs most essentially 

 from the type in not having any carina. Even where the test is present there is 

 no distinct carina — nothing more than a small keel formed by the meeting of the 

 two sides of the ventral area. In respect of ribbing the specimen differs in no 

 way from the type ; in respect of umbilicus but very little. As it is the only 

 specimen of its kind which I have seen, I cannot say whether this condition of the 

 carina is more than accidental ; but no specimens have come under my notice 

 exhibiting anything intermediate between this form and the type with respect to 

 the carina. A prominent carina is one of the easiest characters by which to 

 distinguish the type-form from Ludwigia Murchisonce; but, if the uncarinated 

 specimen be in reality a variety of the type, the value of this character will be 

 diminished. I have not, however, seen the combination of coarse ribs and narrow 

 umbilicus in any varieties of L. Murchisonce. L. Lucyi is, of course, a direct 



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