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Remarks. I am not quite sure that the specimens I have examined represent the 

 full-grown form. Yet the shape of the valves and of the capitulum as a whole are so characteristic 

 that it may be described as a distinct animal. In some regards it approaches D. Warwicki — 

 but the much produced form of the capitulum makes it at once look very different, the shape 

 of the scutum being moreover very peculiar. 



The species is named in compliment to Captain now Commander G. F. Tydeman, the 

 distinguished commander of H. M. S. "Siboga" during its cruise in the Malay Archipelago. 



3. Dichclaspis orthogonia Darwin. PI. II, fig. 14 — 18. PI. Ill, fig. i, lA, iB and 10^. 

 185 1. Darwin, Monograph, Lepadidae, p. 130, pi. II, fig. 10. 



Since Darwin published his Monograph, this species has not been observed so far as 

 I know. Darwin described it from British Museum specimens, habitat unknown. The "Siboga" 

 collected a few specimens, south of Timor, at a depth of i 1 2 m., and again at two other 

 stations, So and ']'], in the Archipelago: I think it very probable that the specimens studied 

 by Darwin had also been collected in the Malay archipelago. 



I had at my disposal a few large and smaller .specimens of this species. The largest 

 has been drawn by me, magnified about 10 times, and is figured PI. II, fig. 14. The capitulum 

 of this specimen measures 6,6 mm., whereas Darwin says that the length of the capitulum is 

 above "/,o"^^ of an inch, 5,1 mm. The other specimens of the "Siboga" are about that size, or 

 still smaller. 



The shape of the valves is much like Darwin's description : I have prepared these valves 

 from a 5 mm. specimen and figured them separately (fig. 15, «, b, c). 



The scutum (fig. 15a) corresponds well with Darwin's description; in the largest 

 specimen however, the occludent segment is less than twice as long as the basal segment. 



The tergum (fig. 15^) shows the four prominences in which the four ridges proceeding 

 from the umbo end. The projection at the occludent margin of the valve is extremely small, 

 smaller perhaps than in the figure given by Darwin. 



The carina (fig. 15^ and fig. 16) terminates in a heart-shaped disc (fig. 16) with a 

 slight excavation in the middle. This excavation in the specimen the valves of which I prepared 

 was neither so deep nor so distinct as Darwin has it in his description. The whole shape of 

 the valve, however, so much resembles D.'s description and figures, that no uncertainty as to 

 its identity could remain. 



Darwin's specimens were in a bad condition ; of the peduncle he said that it was 

 unknown, probably short. The "Siboga" specimens all have a peduncle: it is cylindrical and 

 has about one third the length of the capitulum. 



The different parts of the mouth correspond well with D.\rwin's description. I give a 

 figure of the maxilla (fig. 17) showing the notch (bearing one spine) beneath the three large, upper, 

 unequal spines, and the highly projecting inferior part bearing eight spines in all, one of which 

 (the third) is larger than the other ones. Darwin says that this inferior part is, itself, obscurely 

 divided into two steps — the maxillae of the specimen I dissected did not show this peculiarity. 



SIBOGA-EXPEDITIE XXXI <7. 



