275 DR. P. P. CARPEKTER ON NEW SPECIES 



( = Lepidop?eurus, Add.,) known by the sharp incisor-teeth lying 

 within a projecting lip, there are three types of mantle-margin, 

 which may be conveniently separated as subgenera, to aid in the 

 difficult task of describing and identifying species. The typical 

 forms, for which the name Ischnochiton should be retained, have the 

 scales somewhat chaffy, and very finely striated. I. magdalensis 

 and /. sanguineus well represent the group. But another series have 

 the mantle-scales imbricate and strong, as in Chiton, Gray, ( = Lo- 

 phyrus, Add.,) from which they cannot be distinguished without 

 dissection. For this Messrs. Adams's name Lepidopleurus may be 

 retained in a restricted sense. It is uncertain what l\isso's original 

 genus was meant to include : his diagnosis applies to all Chitons 

 with distinct side-areas and scaly margins. 



A third group, separated by Dr. Gray in his c Guide,' p. 182, as 

 having the " mantle-scales minute, granular," has been named Tra- 

 chydermon : it abounds in the Californian region. 



The specimens of L. adamsii were found among the duplicates 

 named Chiton dispar by the Professor ; one was attached to Discina 

 cumingii. 



LEPIDOPL.EURUS TENUISCULPTUS. 



L. t. "L. adamsii" simili ; olivacea, color e pall ido sen intension 

 minute variegata ; tota superficie minute granulosa ; areut 

 lateralibus vix definitis ; suturis plerumque albido maculatis ; 

 mucrone antico, satis conspicuo, parte postica concava : intus, 

 ut in "L. adamsii " for mat a. 



Variat : t. pallidore, ad jugum rufo-tincta. 



= Chiton dispar, C. B. Ad. no. 373, pars. 



The outside of this shell so much resembles the young of Chito,. 

 (Lophyrus) stokesii, that specimens may have been distributed undei 

 that name. Very few individuals were found. 



ISCHNOCHITON ELENENSIS (diagn. auct.). 



Extus areis centralibus clathris parallelis circ. xx. decussatis , 

 ar. lat. costis ii., validioribus, tumidis, tuberculosis : intus 

 marginibus suturalibus posticis reflexis, tuberculatis, sinu ad 

 jugum parvo ; laminis insertionis unifissis, ad laminas sutu- 

 rales anlicos junctis, sinu latissimo. Valva antica extus costis 

 xii., haud validis ; intus Jissuris x., dentibus acutis, subgrundd 

 parva. Valva postica mucrone subpostico, depresso ; parte 

 postica expansa, concava, costis circ. xi. subobsoletis ; intvs 

 lamina insertionis circ. ix-.-fasa, dentibus curtis, subgrunda 

 parva, intus callosa. 



The central valves in this species are normal ; but the posterior 

 valve offers a transition towards Callochiton, the outside being con- 

 cave posteriorly, the insertion-teeth short and the eaves callous. 



ISCHNOCHITON (? var.) EXPRESSUS. 



I. t. "I. elenensi" simili, sed carnea ; areis centr. clathris x., 



266 



