RANDOM NOTES ON NATURAL HISTORY. 



85 



quarters inch in length, but in Maine they 

 are an inch, and in P^urope one and a half 

 inches long. They are very abundant in 

 Norway, Scotland, and Ireland, where they 

 are used for bait, and in times of scarcity, 

 for food. 



A description of this species is difBcult, 

 as the individuals vary so widely. Shell 

 oblong-oval, elevated ; apex behind the cen- 

 tre, pointed and turned towards the head 

 of the animal ; color greenish-white, with 

 brown stripes ; within, the centre is gener- 

 ally dark brow^n, and the margin checkered 

 with brown and white spots. It resembles 

 in form, though on a larger scale, our com- 

 mon fresh-water limpet, Ancylus fuscus. 

 Its habitat is on stones from low-water 

 mark to twenty fathoms or more. 



There is a variety of this species whose 

 habitat is only on the narrow leaves of 

 Zostera marina (eel grass). Whether this 

 is only a variety of testudinalis or a dis- 

 tinct "species, I am not prepared to say; 

 many authors consider it distinct, and it 

 certainly differs as much in appearance, 

 and more so than some species which are 

 universally acknowledged to be distinct. If 

 the normal testudinalis resembles Ancylus 

 fuscus. Ad., this variety still more resem- 

 bles our other fresh-water limpit, Ancylus 

 parallellus, Hald. The specimens do not 

 vary as much as the testudinalis, but arc 

 very uniform. The shell is long and nar- 

 row, only three-tenths of an inch broad by 

 one-half inch or more in length ; the sides 

 compressed, thin and fragile ; ends obtusely 

 rounded ; color reddish-brown, checkered 

 with yellow oval or circular spots ; the in- 

 terior showing the exterior markings. This 

 species is called Alveus, Conrad, var., or, by 

 those who consider it distinct, Acma?a 

 (Collitsella) alveus. Con. I am disposed to 

 think it a distinct species by itself. 



Order Polyplacophora, Gray. 

 Family 61. Chitonida?, Guilding. The 

 order Polyplacophora differs from the other 

 orders of the sub-class Prosobranchiata in 

 both animal and shell. In this order the 

 sexes are united in each individual, while 

 the shell is multivale, or composed of eight 

 separate transverse plates, inserted in a 

 coriaceous mantle, forming an extended 

 margin around them. There is but one 

 family, as above, and two genera, Chiton 

 and Chitouellus. 



Genus Chiton, Linn^us, 1758. 



The earlier naturalists considered these 

 unique shells to belong to the Malentozoaria 

 of Blainville, or articulated mollusks, and 

 included them among the Barnacles or 

 Crustacae ; they also called them multi- 

 valves. They were deceived by the ap- 

 pearance of the shell, which consists of 

 eight arched plates, but are not valves, as 

 were supposed, nor articulated in any wa^', 

 but arranged like shingles on a roof, and 

 let into the tough mantle of the animal, at 

 the ends, by the sharp, smooth edges. 

 These plates are more or less sculptured, 

 and the margins either bare or covered with 

 hairs, spines, or other ornamentation. They 

 are found in all parts of the world, but un- 

 like most shells, the finest species are not 

 tropical, but inhabit the colder shores of 

 North and South America. There are more 

 than 250 species, divided among about fifty 

 sub-genera. Seven species are credited to 

 New England, of which two are known to 

 inhabit Rhode Island. Possibly some of 

 the others may yet be found here. The 

 two species known to inhabit our bay are 

 as follows : 



68. Chiton (Ch^topleura) apiculatus, 

 Say. 



Shell oblong oval, color grayish ; anterior 

 plate a crescent, with three or four con- 

 centric lines and numerous dots arranged 

 in regular lines along the margin ; the next 

 six plates have on their dorsal triangles, 

 twenty to thirty longitudinal series of beads, 

 or pointed, elevated dots ; on the lateral 

 triangles, which are elevated above the dor- 

 sal ones, are scattered dots like those on 

 the anterior plate ; posterior plate, with the 

 series of dots like those on the dorsal tri- 

 angles of the six central plates, a central 

 tubercle, and the remainder with scattered 

 dots like those on the anterior plate. Mar- 

 gin coriaceous, with alternate stripes of 

 white and dusky pubescence. Length one 

 inch, breadth three-filths. It inhabits from 

 South Carolina to Cape Cod, and is found 

 on stones in dredging and on dead shells of 

 Busycon, Natica, etc. 



69. Chiton (Track ydermon) ruber, Lowe. 



Shell small, oval, elevated, carinated; 

 plates smooth and shining, even under the 

 lens ; color light red, sometimes with flivshes 



