with, I might say, typical specimens of L. nicobarica, other specimens of a form or species of 

 Lithotrya were collected, which after careful study I feel inclined to consider as different 

 from Reinhardt's L. nicobarica. I shall describe the other form as a new species and call it 

 Lithotrya conica-^ as the comparison of the different specimens with one another and with 

 Darwin's description brought to light that more or less interesting differences occur even between 

 the specimens which doubtless belong to the original species of Reinhardt, I think it useful to 

 enter into "some detail on that species first of all. 



With regard to the valves of L. nicobarica the following may be pointed out: 



The scutum has the tergal margin either straight or slightly sinuous, in which case 

 the upper part is hollowed out. 



The carina has a well-developed central, internal ridge which extends over the upper 

 half of the valve. The inner growing surface is in most specimens but very indistinctly pentagonal. 



The rostrum is different in size in the different specimens, the number of zones 

 preserved varying in the 18 specimens I was able to observe from 2 — 7. This number was 2 in 

 three specimens, 3 in ten, 5 in three, 6 in one and 7 in one. The number of the subjacent 

 scales of the peduncle, which the rostrum equals in width, varied from 4 to 7 : it was 4 in four 

 specimens, 5 in five, 6 in seven and 7 in two. In one of the specimens from Pulo Milu, Galatea, 

 which I was able to study more carefully, the number of distinct zones was 3 and the number 

 of scales of the j^eduncle which the rostrum equalled was 7. [In the figure of this species 

 Darwin reproduced after Reinhardt a much greater number of zones is indicated.] 



The latera which according to Darwin are unusually large in this species vary greatly 

 in the different specimens. Their general shape is as described by Darwin: triangular, elongated 

 transversely with the carinal angle a rectangle; but they are much broader in some, narrower 

 in other specimens. I compared the length of this valve with that of the carina and I thus 

 found that it can be less than half as long as that valve and also nearly as long as it: in a 

 specimen the length of the carina in which was 13 mm. the latus measured 11 mm., and its 

 length was 6 mm. in another specimen, the carina of which was 7 mm. long. The number of 

 zones of growth preserved in the specimens I investigated also differed greatly: on iS specimens 

 this number was once 8, twice 7, three times 5, four times 4 and six times 3. In the two 

 remaining specimens the zones of the little valves were quite covered with chalk and could in 

 consequence not be distinguished. The latera as a rule equal in width the seven subjacent scales 

 of the peduncle; in some of the specimens this number, however, is six or five and in one 

 specimen four of the scales equalled the width of this valve. 



With regard to the peduncle the only difference from Darwin's description I noticed 

 was that the shape of the upper scales was more irregular. 



With regard to the body of the animal I may point out the following : 



The labrum has a row of blunt teeth; its palpi have their ends rather more rounded 

 than truncated. 



The mandibles have the distance between the tips of the first and second teeth 7, 

 taking the distance between the tip of the second tooth and the inferior angle as 9. 



The maxillae sometimes have the notch beneath the large upper and two smaller 



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