ORDER AP0DA. 587 



Order III. — Apod a. 



Cirripedia, with the carapace reduced to two separate 

 threads, serving for attachment : body consisting of one ce- 

 phalic, seven thoracic, and three abdominal segments, all 

 destitute of cirri. Mouth suctorial, with the mandibles and 

 maxillae placed bach to back, enclosed in a hood, formed by 

 the union of the labrum and palpi. Metamorphoses un- 

 known. 



The characters above given fully justify, I think, the 

 formation of this order; though it contains only one species, 

 the Proteolepas bivincta. The mere external appearance 

 (PL 25, fig. 7), so wonderfully different from that of every 

 other cirripede, would by itself prompt to this same conclu- 

 sion. At first sight the Proteolepas, if of fresh-water 

 origin, might even have been mistaken for the larva of 

 some insect, fastened by two threads to its prey. The 

 entire absence of the three anterior segments of the head 

 and therefore of the carapace, or, speaking strictly, the mere 

 rudiment of these parts, forming an envelope to the two ce- 

 ment-ducts, — the absence of a stomach, rectum, and anus, 

 — the entire absence of thoracic and abdominal appendages 

 or cirri, — the absence of a probosciformed penis, — are all 

 negative characters, which might ensue from degradation, 

 so common with parasites; and which might, therefore, have 

 been esteemed of not high classificatory value. But the suc- 

 torial mouth, with the palpi andiabrum united into a hood, 

 and with the mandibles and maxillae reversed or turned back 

 to back, so as to be utterly incapable of prehension, is a type 

 of structure not hitherto met with, I believe, in anv other 

 animal, and cannot be explained away by degradation. 

 The formation of the ova within the segments of the body, 

 a peculiarity confined to this one cirripede, evidently 

 results from the non-development of the anterior part of 

 the head, within which the ova are usually formed; out the 

 compound structure of the visicula seminalis is a peculiarity 



