233 



from I ho Lower Silurian of Bohemia. \vliich lie thinks must be a fossil 

 C.rinoid-larva ("fin Pluleus cines Crinoiden"), I In- "Fumi bohemicn" of 

 Barrande 1 ). Hut provided first that it hi- an Kchiiioderm, anybody who 

 has the slightest knowledge of Echinoderm-larvae will sir 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 plales is represented along the whole 

 border of the animal. Hut. moreover, it is certainly no Kchinoderm at all. 

 Professor (.). .laekel, with whom I have discussed this matter, informs me 

 that he knows the "I-'nrcti bohemiai" quite well, and stales that the re- 

 presentation which Frit sch has given of it is quite erroneous. In fad. 

 Professor .laekel does not hesitate in declaring it to be identical with 

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

 Columbia which YValcoll has described 2 ) under the name of Maiclla 

 splcndcns, and which is a Crustacean, probably allied to the Trilobiles. 



As regards the anatomical si rue I ure of the Echinoderm-larvae ( leav- 

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

 may be called to the fad that Ihe 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, Ihus 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 Ihe lower end of the esophagus. It is sometimes 

 very large, as in Ophiopliileus scrralus (bimnciilatiis), sometimes also of a 

 more complicate shape, as in the larva of Coloboceiilroliis dlnilus. This 

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

 Joh. Mii Her in his Memoir "Uber die Ophiurenlarven d. Adrialischen 

 Meeres". p. 1, Taf. I. Fig. 1, and also Me t schnikoff (Op. cil.) has care- 

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

 larva, where il plays an important part during Ihe process of metamor- 

 phosis. Also in a Spalangoid-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 Kchiiwcdrdium corddliim; 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 Kchinoid-larva?, and accordingly some 

 morphological interest is attached to it. 



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



') A. Fritscli. Cln-r i-iiu- Kchinodi'rmi'iilarve aus deni IfnU-rsilnr Hiilnnens. Xool. An/. 

 :<:<. moil. p. 797. 



-I C.h. 1). Walcott. Cambrian (.colony and Paleontology. II. No. ti. Middle Cambrian 

 Hranchiopotlu, Malarostraca, Trilobita. and Mrn.stoinuta. Smiths. Miscell. Coll. Vol. 57. 



mrj. p. I'.rj. il. 'j:. -jt;. 



30 



