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from the Lower Silurian of Bohemia, which he thinks must be a fossil 

 Crinoid-larva ("ein Pluteus eines Crinoiden"), the "Furca bohemica" of 

 Barrande^). But provided first that it be an Echinoderm, anybody who 

 has the slightest knowledge of Echinoderm-larvse will see at a glance that 

 it is quite absurd to speak of a "larva" in a case like this, where a single 

 or double series of distinct marginal plates is represented along the whole 

 border of the animal. But, moreover, it is certainly no Echinoderm at all. 

 Professor 0. Jack el, with whom I have discussed this matter, informs me 

 that he knows the "Furca bohemica" quite well, and states that the re- 

 presentation which Fritsch has given of it is quite erroneous. In fact. 

 Professor Jaekel does not hesitate in declaring it to be identical with 

 the organism from the Middle Cambrian (Stephen formation) of British 

 Columbia which Walcott has described 2) under the name of Marella 

 splendens, and which is a Crustacean, probably allied to the Trilobites. 



As regards the anatomical structure of the Echinoderm-larvse ( — leav- 

 ing the reduced, barrel-shaped forms out of consideration here — ) attention 

 may be called to the fact that the ventral depression of the body, in which 

 the mouth lies, the oral area, generally continues some way down below 

 the upper edge of the anal area, thus forming a cavity, the lower limit 

 of which is mostly very distinctly seen as a line passing across the anal 

 area at about the level of the lower end of the esophagus. It is sometimes 

 very large, as in Ophiopluteus serratus (bimaculatus), sometimes also of a 

 more complicate shape, as in the larva of Colobocentrotus atratus. This 

 "suboral cavity", as I have termed it, was well figured and described by 

 Joh. Miiller in his Memoir "Uber die Ophiurenlarven d. Adriatischen 

 Meeres", p. 4, Taf. I, Fig. 1, and also Metschnikoff (Op. cit.) has care- 

 fully studied this cavity, the "subumbrella" as he names it, in the same 

 larva, where it plays an important part during the process of metamor- 

 phosis. Also in a Spatangoid-larva he has noticed it (Taf. VIII, Fig. 12). 

 The same structure was observed, but apparently not understood, by Mac- 

 Bride in the larva of Echinocardium cordatum; he only mentions it as 

 "two large cavities", one on each side in "the web of skin connecting the 

 post-oral arms." — This cavity has some connection with the question 

 about the origin of the "amnion" of Echinoid-larvse, and accordingly some 

 morphological interest is attached to it. 



In the epidermis of the sunk oral area is found a pair of nerve-streaks, 



1) A. Fritsch. Uber eine Echinodermenlarve aus dem Untersilur Bohmens. Zool. Anz. 

 33. 1909. p. 797. 



") Ch. D. Walcott. Cambrian Geology and Paleontology. 11. No. 6. Middle Cambrian 

 Branchiopoda, Malacostraca, Trilobita, and Merostomata. Smiths. Miscell. Coll. Vol. 57. 

 1912. p. 192. PL 25—26. 



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