INVERTEBRATES. 347 



Messrs. Etheridge and Carpenter have lately published through 

 the Ann. and Mag. Nat. Hist., April, 1882, an interesting paper, 

 "On certain points in the Morphology of the Blastoidea, with descrip- 

 tions of some new Genera and Species," in which they explain the 

 terms which they propose to use in their writings. Their terms are 

 in conformity with those now in use for the Crinoids and other 

 Echinoderms, and it would be of great advantage to science if they 

 were universally adopted by future writers upon Blastoids. In order 

 to give this terminology a wider circulation, and for the better com- 

 prehension of the succeeding descriptions, I give here an abstract 

 of their principal terms. 



The "calyx," according to Etheridge and Carpenter, is composed 

 of the "basals" the "radials" or forked pieces, and the "orals" or 

 deltoid pieces. The suture between basals and radials is the "basi- 

 radial suture;" the more or less strongly marked ridge at the median 

 line of each oral is the "oral ridge." In the forked-shaped radials, 

 the handle of the fork is the "body" of the radial, the two prongs 

 are the "limbs;" between the limbs is the "radial sinus," which is 

 occupied by the "ambulacrum." Of the ambulacral structures, which 

 together fill up the radial sinus to a greater or less extent, the most 

 important is the "lancet-piece," which is excavated lengthwise by the 

 "food-groove or ambulacrum proper." Upon or against it rest the 

 "side-plates," pore-pieces of Roemer; they are marked by minute 

 pits, the "pinnule pits or sockets," which must not be confounded 

 with the marginal pores or "hydrospire-pores." The supplementary 

 pore-pieces of Roemer are the "outer side plates." Beneath the am- 

 bulacral fields are the "interradial systems of lamellar tubes or hydro- 

 spires." The openings of these tubes, if directly on the ventral 

 surface of the calyx as in Cadaster, are called the "hydrospire-slits ;" 

 if they are concentrated beneath the ambulacra as in Orophocrinus,* 

 the gap between the edge of the lancet-plate and the sides of the 

 radial sinus is the "hydrospire cleft." This leads downward into the 

 "hydrospire canal." The canals open externally by the "spiracles," 

 formerly called ovarian openings. The spiracle or spiracles of the 

 anal interradius may be confluent with the anal opening to form 

 the "anal spiracle." The plates covering the mouth and peristome, and 

 which are sometimes continued down the ambulacra covering the food 

 grooves, are the "summit plates or the vault." 



*MEEK and WOBTHEX in defining, in 1869, (Geol. Rep. 111., Vol. V, p. 464) the genus Codon- 

 ites, were evidently not aware that Von Seebach had proposed, in 1864, (JNacnr. Ji. 

 Geselloch. zu Goettingen, p. 110) for Pentremit s gtelliformia Owen and bhum. the genus 

 Orophocrinus. The latter has since been adopted by Ludwig, Zittel and by Mneridge and 

 Carpenter. 



