PELTASTES. 149 



The family Salenid^ commenced their life-career in the lower zone of the Inferior 

 Oolite. Acrosalenia abound in the Inferior Oolite and the Cornbrash ; and one is found in 

 the Coralline Olite. Pseudosalenia was discovered in the Corallian of the Haut Jura. 

 Ileterosalenia is represented by one solitary species in the Chalk with Hippurites (Senonieii 

 Inferieur). Peltmtes and Gonioj^horns are found chiefly in the Lower Cretaceous. Salenice 

 occur in the Lower, Middle, and Upper Cretaceous rocks ; and in the Tertiary Numraulitic 

 limestone of Biarritz, are represented by a curious species, Salenia Pellati, recently found 

 in that formation. Our present seas contain, we are told, a representative form of this 

 family, which was recently dredged up off the American coast by the deep-sea dredging- 

 operations performed in 1869 ; beyond the alleged fact I know nothing whatever of the 

 genus to which this existing form belongs. 



Genus — Peltastes, Acjassiz, 1838. 

 Salenia (pars), Agassiz, 1S3S. Hyposalenia, Desor, 1856. 



Test small, circular, more or less inflated above, and almost flat below ; pores simple 

 in the zone and crowded near the peristome ; ambulacra straight, or slightly flexuous, fur- 

 nished with two rows of small, close-set, homogeneous mammillonated granules. Inter- 

 ambnlacra large, provided with two rows of large, crenulated, imperforate tubercles. 



Mouth-opening moderate in size, peristome divided into unequal lobes by feeble 

 incisions. Periprocte excentral and posterior, situated in the line of the animal's axis. 

 Apical disc shield-shaped, composed of large plates, more or less undulated at the 

 border; the disc covers in general a large portion of the upper surface of the test, and 

 is marked by sutural impressions and striae that vary in the different species ; the right 

 antero-lateral ovarial plate has an oblong fissure always directed from right to left, 

 corresponding to the oviductal pore and representing the madreporiform body. 



Peltastes in its general form and structure resembles Salenia ; it is distinguished from 

 the latter, however, by the position and direction of the periprocte, which is excentral, 

 and directed obliquely backwards and outwards and towards the right side ; the ambulacra 

 likewise are less flexed, the mouth-opening is smaller and lies in a deeper depression ; 

 the madreporiform fissure in the right antero-lateral ovarial plate is smaller. 



The genus Peltastes was established in 1838 by Professor Agassiz j and in 184G 

 MM. Agassiz and Desor comprised in the genus all the Saleniad^ in which the periprocte 

 was situated in a line with the axis of the animal, and this forms the leading character 

 by which it is distinguished from Salenia. 



The genus Peltastes is special to the Cretaceous formations; it commences with some 

 remarkable forms in the Lower Greensand, appears in full force in the Upper Greensand and 

 Lower Chalk; becomes rare in the Upper Chalk, and finally disappears from its upper stages. 



