20 



EAST COAST MARINE SHELLS 



and known as the CAPITULIFORM TOOTH, often 

 shaped like the blade bone of a shoulder of 

 mutton. The central tooth is present and 

 often small. 



(g) DOCOGLOSSA. Compared with the 

 Rhlpidoglossa the members of this group 

 nossess a radula with a few strong teeth. 



Only three fam- 

 ilies, Acmaeidae, 

 Patellidae (Fig. 

 S8) and Lepetidae 

 are placed here. 

 The number of 

 teeth in a row 

 range from two to 

 twelve. The rib- 

 bon is often very- 

 long, the teeth 

 heavy, deep-horn 

 color, and some- 

 what opaque. The 

 arrangement is 

 somewhat compli- 

 cated with a mvil- 

 tiplication of 

 identical cen- 

 trals. In some 

 cases there is no 

 true central 

 tooth. Lateral 

 and marginal 

 teeth may be lost, 

 when present they 

 are few in num- 

 ber. 



Outside 

 of the Gastropoda, 

 which have Just 

 been discussed, 

 the radula occurs 

 in the Amphineura 

 or coat-of-mail 

 shells. In these 

 it is unique, be- 

 ing composed of 

 thick and deeply 

 colored teeth, 

 greater in number 

 than in the Docoglossa. In the Scaphopoda, 

 or tusk shells, the radula is large and pe- 

 culiar. It occurs in Dentalium with a 

 broad plate representing the central tooth. 

 The one lateral tooth is robust, arched, 

 and a little cusped; the marginal a large 

 quadrangular plate, quite simple. The 

 formula for the Scaphopoda would be 



Fig. 28 

 Radula of Patella 

 Patella vulgata L., showing 

 the normal position of the 

 radula, which is doubled 

 back in a bow; the shell has 

 been removed, and the whole 

 visceral mass is turned for- 

 ward, exposing the dorsal 

 surface of the muscular foot; 

 gr, longitudinal groove on 

 this surface; i, i, intes- 

 tine; 1, liver; m, m, mantle 

 edge; mu, muscles (cut 

 through) fastening the vis- 

 ceral mass to the upper 

 sides of the foot; ov, ovary; 

 r, radula; u.f, upper or dor- 

 sal surface of the foot. 



1.1.1.1.1. Among the Cephalopods the radu- 

 la is^of a singular uniformity. It is al- 

 ways small, with a central tooth, a few 

 marginal and very few lateral teeth. 



Localities 



In the descriptions of the various 

 species the range Indicated is in each case 

 inclusive; thus Maine to Florida indicates 

 that an individual species has been record- 

 ed from both Maine and Florida, besides in- 

 termediate points. (See Map of Florida, 

 page 301.) 



A solitary beach specimen, without 

 the living animal, might easily be carried 

 by the sea a long distance. The presence 

 of several beach specimens together usual- 

 ly Indicates that the species is living 

 somewhere nearby. 



The temperature of the sea water 

 largely affects mollusks. The species liv- 

 ing in shallow water of Maine or Canada, at 

 a given temperature may occur in the south 

 in much deeper water where the temperature 

 is similar. 



It will be noted that the figures 

 include a number of shells from distant lo- 

 calities. These species also occur upon 

 the coasts of the United States. It has 

 been impossible to illustrate local materi- 

 al in every case but usually the figures 

 will make identifications possible. 



Dimensions of Specimens 



The size of individuals is an im- 

 portant matter In making comparisons of the 

 various species. Many are very constant in 

 the over-all length of the shell and the 

 dimensions often furnish a clue in making 

 an Identification. However, the size is 

 often influenced by the temperature of the 

 water and the food supply. These matters 

 should be taken into consideration and due 

 allowance made. For example West Indian 

 specimens often are larger and more bril- 

 liantly colored than the same forms living 

 well up the continental coast. 



The figures on the plates are drawn 

 or photographed to different scales. In the 

 explanations of the plates, and in the text, 

 the figures refer to the greatest dimension, 

 length or width of the shell, not the ani- 

 mal. One millimeter is about one twenty-fifth. 



