the Morphology and Classification of the Saleaiidoe. 129 



cesses sometimes uniting. Spines large and small, the former 

 striated longitudinally, or plain, and often not quite circular 

 in transverse section ; smaller spines striated. 



Distribution. Fossil: Lias toNeocomian, England, Europe, 

 and North Africa. 



It will have been observed that Acrosalenia is the oldest of 

 the iSaleniidfe and that its species are more complex than 

 those of any other genus of the family. The frequent per- 

 fection of the dorso-central plate, the existence of compound 

 plates in the ambulacra, the well-developed branchial cuts, 

 and the ridges and processes of the perignathic girdle separate 

 the genus from the Cidaridfe, and it is more distinct from 

 that family than are the genera Peltastes and Salenia. 



Tliese last-named genera can hardly liave had an Acro- 

 salenian ancestry. Acrosalenia became extinct before Salenia 

 attained much importance, but there was a Peltastes with 

 Acrosalenian affinities in the time of the Oolite. 



Genus Peltastes, Agass. 



The oldest species of the Peltastes-gYou^ is a true Peltastes 

 in all the characters but one, and that is remarkable, for the 

 primary tubercles of the interradia are perforate as well as 

 crenulated. 



There are several specimens of this species from the Coral- 

 lian of Wurtemberg, and the locality Nattheim, in the British 

 Museum, and they correspond with Acrosalenia inter punctata^ 

 Quenst. (Petref. p. 576 (old edition), pi. xlix. figs. 5 and 6). 

 The test is depressed and the apical system is large ; the 

 basals are large, the posterior unusually so, and the dorso- 

 central is comparatively small. The periproct is directly 

 posterior. The ambulacra are narrow, wavy, and have two 

 rows of small secondary tubercles, so closely placed that 

 nothing is seen between them along the median suture. The 

 pores are moderately numerous, in simple series, and there is 

 a pair to each plate, and there are no primary plates joined to 

 form compound plates, but every plate is separate, as in Pel- 

 tastes and Salenia. Neither the apical nor the ambulacra! 

 development is that of Acrosaletiia. 



The primary tubercles of the interradia are large and have 

 perforate mamelons and crenulated bases. The branchial 

 cuts are small. Quenstedt noticed its many-sided character, 

 and it is now necessary to place the form as follows :-— 



Peltastes interpunctatus, Quenst., sp. 



Jurassic. 



Ann. & Mag. N. Hist. Ser. 5. Vol. xix. 9 



