PLATE 7. 



Arbacia punctulata (Lamarck). 



Fig. 1. Woods Hole, Massachusetts. Diam. 11 mm. R. T. J. Coll., 785. X 3.8. A partially tetramerous specimen; 

 there are four ambulacra, but all other parts are in fives. Ambulacrum IV is wanting, so that interambulacra 3 and 4 

 are in contact throughout; extra interambulacra] plates are developed as space fillers in this area. Page 41. 



Toxopneustes variegatus (Lamarck). 



Fig. 2. Tampa Bay, Florida. Measures 67 mm. through the axis II, 4. R. T. J. Coll., 749. X 1.9. Partially tetramer- 

 ous; five ambulacra and interambulacra ventrally, dorsally above the ambitus there are four ambulacra, interam- 

 bulacra and oculars, but five genitals. Ocular II lies just below the ambitus and to it extend ambulacrum II, the 

 right half of interambulacrum 1, and the left half of interambulacrum 2. Above this zone the left half of inter- 

 ambulacrum 1 and the right half of interambulacrum 2 are in contact to the apical disc, where they abut against 

 oculars I and II as usual. (Compare p. 35; Plate 6, figs. 1, 9; text-fig. 218, p. 191.) Page 42. 



Strongylocentrotus drbbachiensis (O. F. Muller). 



Fig. 3. York Harbor, Maine. Diam 37 mm. R. T. J. Coll., 662. X 5. Almost completely tetramerous, with four 

 teeth, eight primordial ambulacral plates, four ambulacra, and interambulacra, four oculars, but five genitals. Geni- 

 tal 1 is a depauperate imperforate plate lying between ocular I and genital 2. The absent parts are ocular and 

 ambulacrum II, the right half of interambulacrum 1 and the left half of interambulacrum 2. Oculars I, V are insert 

 as usual. An extra pore occurs in genital 4. (Compare Plate 6, figs. 1, 9.) Page 40. 



Fig. 4. York Harbor, Maine. Diam. 17 mm. R T. J. Coll., 786. X 3.7. Partially tetramerous; ventrally there are 

 five teeth, ambulacra and interambulacra, dorsally only four ambulacra, but the interambulacra and other parts are 

 in fives. Ocular II is imperforate, ambulacrum II exists for only a short distance ventrally, above which inter- 

 ambulacra 1 and 2 are in contact, and some extra interambulacral plates are developed as space fillers. An accessory 

 plate (split off?) lies between oculars I, II and genitals 1, 5. Page 43. 



Fig. 5. York Harbor, Maine. Diam. 51 mm. R. T. J. Coll., 784. X 2.8. Partially tetramerous; ventrally there are 

 five teeth, in the corona five ambulacra, but only four interambulacra, also four oculars and genitals. Ocular II 

 may be considered double as it has two pores related apparently to ambulacra I and II. There is no trace of inter- 

 ambulacrum 1; ambulacra I and II are in contact throughout their extent. Page 41. 



Fig. 6. Frenchman's Bay, Maine. Diam. 36 mm. R. T. J. Col!., 783. X 3. Genital 3 is split by one horizontal suture, 

 and genital 2 is split into three plates. (Compare Eehinothuriidae.) Page 168. 



Fig. 7. Dumpling Islands, North Haven, Maine. Diam. 14 mm. R. T. J. Coll., 848. Completely hexamerous specimen, 

 the apical disc. X 7.7. Six ambulacra, interambulacra, oculars and genitals, but genitals 3 and 6 are fused. The 

 added parts lie between oculars III and IV. (Compare Plate 6, fig. 2; Plate 8, fig. 3.) Page 47. 



Fig. 8. Same specimen, peristome. X 4. There are six teeth, twelve primordial ambulacral plates and actinal cuts, 

 six ambulacra and interambulacra. Page 47. 



Echinarachnius parma (Lamarck). 



Fig. 9. Chelsea Beach, Massachusetts. Diam. 60 mm. Boston Soc. Nat. Hist. Coll., 348. X 1.4. Partially hexamer- 

 ous; there are five ambulacra and interambulacra ventrally, six ambulacra and interambulacra dorsally; the added 

 areas lie between interambulacrum 1 and ambulacrum II. In the basicoronal row the five primordial interambulacral 

 plates and the ten primordial ambulacral plates are in place as usual. Of the latter, the la, Ha, III6, IVa, V6 are 

 larger as usual by LoveVs law. Same specimen as photograph, Plate 8, fig. 4. Page 49. 



