' 140 



when the grooves appear to terminate. I would suggest the 

 probability that in the juvenile stage some evidence of slits 

 may exist and disappear in the mature or senile form. 



Classification. — While it is to be greatly regretted that 

 the animal and radula are missing, and also that permission 

 has not been obtained to disarticulate some of the valves,, 

 the transparency of the shell has made this latter less im- 

 portant than is usually the case, I have been able to note 

 sufficient features to justify one in removing the genus 

 Choriplax ( = Microplax) out of its setting in our previous 

 classification. I can see no justification for placing a species 

 with abnormally developed insertion plates under the Lepido- 

 pleuridae. Had the animal been present and the valves dis- 

 articulated, there would have been but little difficulty in finding 

 its true place in the Natural System or Taxis. In spite of these 

 limitations, the characters that it has been possible to observe 

 are sufficient to warrant our placing the genus Choriplax, 

 Pils., near the genus Amictda, Gray. For reasons given 

 hereunder I should place it between Amictda and the Sub- 

 family Cryptochitoninae. The characters of the genus 

 Amictda, Gray, are given by Pilsbry (in Man. Con., vol. xv., 

 p. 43) as "Valves almost covered by the extension of the 

 girdle over them, leaving only a small, rounded, or heart- 

 shaped portion exposed at the apex of each; posterior borders 

 of valves produced backwards in rounded lobes at each side:, 

 the lobes completely separated by a posterior sinus having the 

 tegmentum at its apex. Posterior valve having a posterior sinus 

 and one slit on each side. Girdle more or less pilose, often hav- 

 ing pore rows. The essential features of Amicula are its small 

 exposed portion or tegmentum, situated at the posterior edge, 

 and not extending forward to the sinus, its mopaloid posterior 

 valve, short contour, and short gills." 



The species under consideration corresponds with Amicula 

 in some of its most striking features, but, although like the 

 Amicula, the tegmentum does not extend forward to the 

 sinus ; unlike that genus it does not extend to the posterior 

 margin, neither have we noticed any slit, nor is the girdle 

 pilose. 



The description of the Cryptochitoninae, in the same 

 work, p. 48, is: "Valves entirely concealed in the leathery 

 girdle and lacking tegmentum ; their posterior margin pro- 

 duced backwards in a deep lobe on each side, the lobes united 

 across the median line, causing the apices of all valves to be 

 removed inwards from the posterior edge, slits sub-obsolete 

 or lacking in the intermediate valves, girdle covered with 

 minute tufts or bristles." It will be noticed that two of the 

 distinguishing features of the Cryptochitoninae are present in 



