275 DR. p. p. CARPENTER ON NEW SPECIES 



( = Lepidopleurus, 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 u&me Ischnochiton should be retained, have the 

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

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

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

 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 Risso'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 ' 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 Biscina 



Lepidopi,eurtjs tenuisculptus. 



L. t. "L. adamsii" simili ; olivacea, colore pallido seu intensior^ 

 minute variegata ; tota superflcie minute granulosa ; arecs 

 lateralibus vix dejinitis ; suturis plerumque albido maculatis ; 

 mucro?ie antico, satis conspicuo, parte postica concava : intus, 

 ut in "h. adamsii " ybrma^a. 



Variat : t. pallidore, adjugum rufo-tincta. 



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



The otitside of this shell so much resembles the young of Ghitor. 

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

 that name. Very few individuals were found. 



ISCHNOCHITON ELENENSIS (diagU. aUCt.). 



Extus areis centralibus clathris parallelis circ. xx. decussatis , 

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

 marginibus suturalibus posticis reflexis, tuberculatis, sinu ad 

 jugum parvo ; laminis insertionis unifissis, ad laminas sufn- 

 rales anticos jimctis, 'sinu latissimo. Valva antica extus costis 

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

 parva. Valva postica mucrone subpostico, depresso ; parte 

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

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

 parva, intus cajlosa. 

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

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

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



ISCHNOCHITON (? Var.) EXPRESSUS. 



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



266 * 



