NO. 5 CLARK : ECHINI OF WARMER EASTERN PACIFIC 227 



Idiobryssus coelus Galapagos Islands 



Meoma grandis Panamic, Western Mexico 



Gonimaretia laevis southern California and Gulf of 



California 



Lovenia cordiformis Panamic, Western Mexico, 



southern California 



Aside from the light thrown on the distribution of the known Echini 

 in the Eastern Pacific, the Velero has collected an abundance of material 

 useful in delimiting the known species, and revealing the existence of 11 

 forms which appear to require names as they do not fit too well into the 

 series of species now known. One of these is a Cidarid and one a Clype- 

 aster, but others are Scutellids of the well-known genera Dendraster and 

 Encope. Never before have such large numbers of specimens been avail- 

 able for comparative study, and it is not strange that new and perplexing 

 forms occur which require designation. Quite likely more material from 

 the coasts of southern Mexico, Costa Rica, Nicaragua, and Panama will 

 indicate different and more correct grouping, but it is believed that the 

 specific limits here suggested indicate a step forward in our knowledge of 

 these multiform genera. 



The naming and describing of new species, however, is only one prod- 

 uct of the Velero's extraordinary collecting. Equally important is the 

 accumulation of immature and very young individuals showing stages in 

 the development of the adult which throw light on evolutionary processes. 

 The most striking of these is exhibited in the growth changes of young 

 Spatangus, a genus represented by but one species in the Eastern Pacific, 

 widely separated from its congeners in Europe, Asia and Africa. The 

 Velero first met with Spatangus in 1936 in the Gulf of California but later 

 collections showed that the vicinity of the Channel Islands in depths of 35- 

 225 fms is the real home of this interesting sea-urchin. Considerably more 

 than two hundred specimens are in the collection and quite a number are 

 young, including some very early stages of development, only about 3 mm 

 long. In these very small individuals there is no indication of either petals 

 or pores. When the individuals are 8 or 9 mm long the petals are indi- 

 cated by more definite outlines and slight depressions, but there are no 

 pores. After the length exceeds 10 mm, the petals can be distinguished 

 more or less definitely and pores are visible at the apical end of the ambu- 

 lacra. But the pores are single and the petals evidently are not sunken at 

 all. There is thus a Palaeotropus stage of development shown which is 

 usually passed through before the Spatangus is 12 mm long. In some 



