258 PALLOCHITON. 



?? Chiton pwuticukstui REEVE, Conch. Icon., Chiton, no. 69 (in 

 part.) 



The posterior terminal mucro, leathery girdle, and beaded sculpt- 

 ure well distinguish this species. The coloring of some specimens 

 (such as those from S. Ignacio Lagoon, Lower California, represented 

 by fig. 1, 6) is of exquisite delicacy. Old individuals generally lose 

 the pustules of the surface except at the base of the valves. One of 

 Reeve's illustrations (fig. 69a) is said to represent a specimen of this 

 species ; but as the other (fig. 696) is certainly an Onithochiton, and 

 as the description indicates that rather than the Pallochiton, I 

 have preferred to retain Carpenter's name for this species. 



A peculiarity of coloring not mentioned in the description is the 

 vertical white stripe extending down the posterior slope from the 

 mucro of the tail valve. In the great number of individuals 

 examined by me I have never found this lacking. 



Section ARTHURIA Carpenter, 1882. 



Arthitria CPR. MS., in BALL, Proc. U. S. Nat. Mus. 1881, pp. 

 284, 287 (Jan. 20, 1882). Type A.filosa Cpr. 



Shell thin ; valves waved ; mucro posterior, produced. Insertion 

 plates acute, smooth, projecting forward in the posterior valve ; 

 sinus flat, laminate, smooth. Girdle leathery, smooth or downy. 

 (Cpr., MS.) 



This section seems to present no characters separating it from 

 Pallochiton. I have not seen the type and only species, and it has 

 not been figured. Comparisons should be made with Pallochifon 

 lanuginosus Cpr. 



P. i ILOSUS Carpenter, n. sp. 



Shell oval, subelevated, the dorsal ridge acute; mucro posterior, 

 hardly terminal, elevated on a strong marginal ridge, the outline in 

 front of it concave. Intense or pale olivaceous. 



Valves delicate, rounded at the margin, making deep sutures. 

 Central areas haiing about 13 distant, beaded subparallel threads on 

 each side, sometimes obsolete, and closer and subacute upon the ridge. 

 Lateral areas moderately defined, and together with the end valves 

 having irregularly scattered rounded granules. 



Interior: anterior valve having 10, central 1, posterior valve 9- 



10 slits ; teeth of the posterior valve solid, acute at the edge, strongly 



ned forward, the slits sloping; the other valves having very 



