THE MYHIAl'ODA OF NORTH AMERICA. 



191 



family Craspedosomida; includes both the subfamilies Lysiopetalidse and Craspedosomida; 

 of Newport, although these are placed by the latter in different families. Whether these 

 two groups belong together or not T cannot say, since I have never seen a specimen of the 

 Craspedosomidai of Newport, The Lysiopetalid'se, as defined in this memoir, includes 

 that of Mr. Newport, but whether it reaches still further I cannot certainly say, on account 

 of the differences in the characters used. The distinguishing mark of the Polydesmidse 

 is commonly supposed to be the possession of lateral lamina or side plates. Now, on 

 glancing over a selected series of specimens, it will be seen that there is a regular grada- 

 tion in size, from the largest lateral lamina to those which are merely rudimentary. 

 Further, in some species of Lysiopetalidse, the whole surface is strongly keeled, and the 

 keel corresponding in position to the lateral lamina is so enlarged as to equal in size the 

 smaller lateral lamina. The groups thus coming, as regards this character, in contact, or 

 at least very close proximity. 



If a segment of a species of each of the three groups is examined, it will be found that 

 fixed characters can be drawn from the varying development of the sterna of the subsog- 

 ments. In the Polydesmidse both of the sterna are thoroughly developed, so that the 

 segment constitutes a perfect ring. In the Julidse the sterna of the posterior subsegments 

 are atrophied, so that each segment is emarginate posteriorly. In the Craspedosomida- 

 both sterna are reduced to their minimum, and not consolidated with the scuta, so that 

 the ring is left altogether incomplete. I have placed the Polydesmidse below instead of 

 above- the other families, because they have both the organs of special sense and the loco- 

 motory apparatus least developed. 



Ord. LYSIO PET ALII ) , K. 

 Sterna minima, cum scutis haud oonjunota. 

 Sterna very small, not conjoined with the scuta. 



There is much obscurity hanging around the genera of this family ; so much that, in the 

 absence of known representatives and types, it is impossible to clear it up. 



Genera, with precisely opposite characters, families widely separated, have been tor- 

 tured out of what claims to be one species. 



In "Europe Meridionale," M. Ilisso described a genus under the name of Calipus, 

 the type of which is a European species, which, M. Gervais says, belongs to the genus 

 Lysiopetalum. Risso's generic characters apply nearly equally well to any Chilognath. 

 Yet, if Gervais is right, his name should have the preference. In Recueil (p. 42), M. 

 Brandt indicated the genius Lysiopetalum, and afterwards (p. 90), the genus Spirostre- 

 phon. The description of the former is mostly made up of what 1 consider family cha- 



