2G0 BULLETIN OF THE 



EXPLANATION OF PLATES. 



Note. — Of these seven plates, all printed by photolithography, the two first are by the Helio- 

 type process of Boston ; the five la^ by the Alberttype, of New York. Although they have the 

 advantage of giving exactly the outlines of the original india-ink drawings, they are very inferior to 

 the drawings themselves ; and not only those, but all similar plates I have seen, are faulty in their 

 blurred outlines and their uneven and spotted shading Their general effect is that of a lithograph 

 from a worn stone. Doubtless the process will, before long, be perfected ; but at present it lacks 

 much. 



PLATE I. 



Diagrams. 



To make clear the terms commonly used in describing Ophiurans, and to show 

 the varied forms of the parts to which these terms apply, there are given two dia- 

 grams, Figs. 1 and 2, representing the under and the upper surface of a disk, with 

 the bases of arms. Each surface is divided into live equal sections, exhibiting the 

 types of as many genera; while the oases of the arms may either correspond, or 

 may belong to others ; so that, in the two- diagrams, there are nine genera, as fol- 

 lows : A, Ophiura ; 15, Ophiocoma ; C, Qphiomyxa ; 1), Ophiothrixj E, Ophioyly- 

 ])ha ; F, disk of Amphiura; G, arm of Ophiopsammium ; II, arm of Hcmicuryale ; 

 I, arm of Ophiomusium. 



Fig. 3 is a diagram of one of the five angles of the mouth, seen diagonally from 

 below, to show the relations of the chewing apparatus, mouth-tentacles, mouth- 

 shields, and jaws. 



Fig. i is a diagram of the mouth parts in Ophioghjplia, showing half of an an- 

 gle, with the under arm-plates of two joints. 



To these figures the same lettering is applied. 



a. Scutum buccal V ; mouth-shield ;' nitindschild ; plaque buccale. This plate 

 is always present, though sometimes quite shrouded by a thick skin (Ophiomyxa). 

 Sometimes it takes on a great development, running far out into the interbrachial 

 space (some species of Ophioghjplia) ; in Ophiarachna it has a small supplement- 

 ary piece lying outside of it. One of the five shields is the madreporic, and is 

 connected with the stone-canal. 



b. Scutclla adoralia ; side mouth-shields. These are lettered in Figs. 8, 4, and 

 will be seen inside the point of the mouth-shield in Fig. 1. Often they may be 

 covered either by thick skin (Ophiomyxa) or by granulation (Oj)hiura). Their 

 size is considerable in Ophioglyjrfia (Fig. 1, E), but in' Ophiothrix they are small 

 and narrow (Fig. 1, ]>). Usually their outer end rests against the innermost side 

 arm-plate ; but in some species of Ophiactis they extend farther, and touch their 

 outer ends at the outer corner of each mouth-slit ; thus forming an unbroken ring 

 round the mouth. 



c. Scutclla urn] in ; jaws ; mundeckstiick (sometimes included in mouth -frames). 

 These are the only pieces of the skeleton not covered by the tegument or its 



